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diff --git a/Source/WebCore/Modules/mediasession/MediaSession.cpp b/Source/WebCore/Modules/mediasession/MediaSession.cpp
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+++ b/Source/WebCore/Modules/mediasession/MediaSession.cpp
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+/*
+ * Copyright (C) 2015 Apple Inc. All Rights Reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "MediaSession.h"
+
+#if ENABLE(MEDIA_SESSION)
+
+#include "Chrome.h"
+#include "ChromeClient.h"
+#include "Event.h"
+#include "EventNames.h"
+#include "HTMLMediaElement.h"
+#include "MediaSessionManager.h"
+#include "Page.h"
+
+namespace WebCore {
+
+MediaSession::MediaSession(Document& document, Kind kind)
+    : m_document(document)
+    , m_kind(kind)
+{
+    // 4. Media Sessions
+    // 3. If media session's current media session type is "content", then create a new media remote controller for media
+    //    session. (Otherwise media session has no media remote controller.)
+    if (m_kind == Kind::Content)
+        m_controls = MediaRemoteControls::create(document, this);
+
+    MediaSessionManager::singleton().addMediaSession(*this);
+}
+
+MediaSession::~MediaSession()
+{
+    MediaSessionManager::singleton().removeMediaSession(*this);
+
+    if (m_controls)
+        m_controls->clearSession();
+}
+
+MediaRemoteControls* MediaSession::controls()
+{
+    return m_controls.get();
+}
+
+void MediaSession::addMediaElement(HTMLMediaElement& element)
+{
+    ASSERT(!m_participatingElements.contains(&element));
+    m_participatingElements.add(&element);
+}
+
+void MediaSession::removeMediaElement(HTMLMediaElement& element)
+{
+    ASSERT(m_participatingElements.contains(&element));
+    m_participatingElements.remove(&element);
+
+    changeActiveMediaElements([&]() {
+        m_activeParticipatingElements.remove(&element);
+    });
+
+    if (m_iteratedActiveParticipatingElements)
+        m_iteratedActiveParticipatingElements->remove(&element);
+}
+
+void MediaSession::changeActiveMediaElements(std::function<void(void)> worker)
+{
+    if (Page *page = m_document.page()) {
+        bool hadActiveMediaElements = MediaSessionManager::singleton().hasActiveMediaElements();
+
+        worker();
+
+        bool hasActiveMediaElements = MediaSessionManager::singleton().hasActiveMediaElements();
+        if (hadActiveMediaElements != hasActiveMediaElements)
+            page->chrome().client().hasMediaSessionWithActiveMediaElementsDidChange(hasActiveMediaElements);
+    } else
+        worker();
+}
+
+void MediaSession::addActiveMediaElement(HTMLMediaElement& element)
+{
+    changeActiveMediaElements([&]() {
+        m_activeParticipatingElements.add(&element);
+    });
+}
+
+bool MediaSession::isMediaElementActive(HTMLMediaElement& element)
+{
+    return m_activeParticipatingElements.contains(&element);
+}
+
+bool MediaSession::hasActiveMediaElements() const
+{
+    return !m_activeParticipatingElements.isEmpty();
+}
+
+void MediaSession::setMetadata(const std::optional<Metadata>& optionalMetadata)
+{
+    if (!optionalMetadata)
+        m_metadata = { };
+    else {
+        auto& metadata = optionalMetadata.value();
+        m_metadata = { metadata.title, metadata.artist, metadata.album, m_document.completeURL(metadata.artwork) };
+    }
+
+    if (auto* page = m_document.page())
+        page->chrome().client().mediaSessionMetadataDidChange(m_metadata);
+}
+
+void MediaSession::deactivate()
+{
+    // 5.1.2. Object members
+    // When the deactivate() method is invoked, the user agent must run the following steps:
+    // 1. Let media session be the current media session.
+    // 2. Indefinitely pause all of media session’s audio-producing participants.
+    // 3. Set media session's resume list to an empty list.
+    // 4. Set media session's audio-producing participants to an empty list.
+    changeActiveMediaElements([&]() {
+        while (!m_activeParticipatingElements.isEmpty())
+            m_activeParticipatingElements.takeAny()->pause();
+    });
+
+    // 5. Run the media session deactivation algorithm for media session.
+    releaseInternal();
+}
+
+void MediaSession::releaseInternal()
+{
+    // 6.5. Releasing a media session
+    // 1. If current media session's current state is idle, then terminate these steps.
+    if (m_currentState == State::Idle)
+        return;
+
+    // 2. If current media session still has one or more active participating media elements, then terminate these steps.
+    if (!m_activeParticipatingElements.isEmpty())
+        return;
+
+    // 3. Optionally, based on platform conventions, the user agent must release any currently held platform media focus
+    //    for current media session.
+    // 4. Optionally, based on platform conventions, the user agent must remove any previously established ongoing media
+    //    interface in the underlying platform’s notifications area and any ongoing media interface in the underlying
+    //    platform's lock screen area for current media session, if any.
+    // 5. Optionally, based on platform conventions, the user agent must prevent any hardware and/or software media keys
+    //    from controlling playback of current media session's active participating media elements.
+    // 6. Set current media session's current state to idle.
+    m_currentState = State::Idle;
+}
+
+bool MediaSession::invoke()
+{
+    // 4.4 Activating a media session
+    // 1. If we're already ACTIVE then return success.
+    if (m_currentState == State::Active)
+        return true;
+
+    // 2. Optionally, based on platform conventions, request the most appropriate platform-level media focus for media
+    //    session based on its current media session type.
+
+    // 3. Run these substeps...
+
+    // 4. Set our current state to ACTIVE and return success.
+    m_currentState = State::Active;
+    return true;
+}
+
+void MediaSession::handleDuckInterruption()
+{
+    for (auto* element : m_activeParticipatingElements)
+        element->setShouldDuck(true);
+
+    m_currentState = State::Interrupted;
+}
+
+void MediaSession::handleUnduckInterruption()
+{
+    for (auto* element : m_activeParticipatingElements)
+        element->setShouldDuck(false);
+
+    m_currentState = State::Active;
+}
+
+void MediaSession::handleIndefinitePauseInterruption()
+{
+    safelyIterateActiveMediaElements([](HTMLMediaElement* element) {
+        element->pause();
+    });
+
+    m_activeParticipatingElements.clear();
+    m_currentState = State::Idle;
+}
+
+void MediaSession::handlePauseInterruption()
+{
+    m_currentState = State::Interrupted;
+
+    safelyIterateActiveMediaElements([](HTMLMediaElement* element) {
+        element->pause();
+    });
+}
+
+void MediaSession::handleUnpauseInterruption()
+{
+    m_currentState = State::Active;
+
+    safelyIterateActiveMediaElements([](HTMLMediaElement* element) {
+        element->play();
+    });
+}
+
+void MediaSession::togglePlayback()
+{
+    safelyIterateActiveMediaElements([](HTMLMediaElement* element) {
+        if (element->paused())
+            element->play();
+        else
+            element->pause();
+    });
+}
+
+void MediaSession::safelyIterateActiveMediaElements(std::function<void(HTMLMediaElement*)> handler)
+{
+    ASSERT(!m_iteratedActiveParticipatingElements);
+
+    HashSet<HTMLMediaElement*> activeParticipatingElementsCopy = m_activeParticipatingElements;
+    m_iteratedActiveParticipatingElements = &activeParticipatingElementsCopy;
+
+    while (!activeParticipatingElementsCopy.isEmpty())
+        handler(activeParticipatingElementsCopy.takeAny());
+
+    m_iteratedActiveParticipatingElements = nullptr;
+}
+
+void MediaSession::skipToNextTrack()
+{
+    if (m_controls && m_controls->nextTrackEnabled())
+        m_controls->dispatchEvent(Event::create(eventNames().nexttrackEvent, false, false));
+}
+
+void MediaSession::skipToPreviousTrack()
+{
+    if (m_controls && m_controls->previousTrackEnabled())
+        m_controls->dispatchEvent(Event::create(eventNames().previoustrackEvent, false, false));
+}
+
+void MediaSession::controlIsEnabledDidChange()
+{
+    // Media remote controls are only allowed on Content media sessions.
+    ASSERT(m_kind == Kind::Content);
+
+    // Media elements belonging to Content media sessions have mutually-exclusive playback.
+    ASSERT(m_activeParticipatingElements.size() <= 1);
+
+    if (m_activeParticipatingElements.isEmpty())
+        return;
+
+    HTMLMediaElement* element = *m_activeParticipatingElements.begin();
+    m_document.updateIsPlayingMedia(element->elementID());
+}
+
+}
+
+#endif /* ENABLE(MEDIA_SESSION) */