[Backport] Reset the last known mouse mousing on MouseLeave

Reset the last known mouse position to be unknown when we get a mouse
leave or when the target of an iframe changes.

BUG=788690

Reviewed-on: https://chromium-review.googlesource.com/814696
Reviewed-by: Navid Zolghadr <nzolghadr@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522877}

Change-Id: Ia02e3a554cb14a7c32ce81308ff82f80cfab392d
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

3 files changed, 8 insertions, 1 deletions

diff --git a/chromium/third_party/WebKit/Source/core/input/EventHandler.cpp b/chromium/third_party/WebKit/Source/core/input/EventHandler.cpp
index 145809951bf..fd1038dc2ee 100644
--- a/chromium/third_party/WebKit/Source/core/input/EventHandler.cpp
+++ b/chromium/third_party/WebKit/Source/core/input/EventHandler.cpp
@@ -893,6 +893,8 @@ WebInputEventResult EventHandler::HandleMouseMoveOrLeaveEvent(
       last_mouse_move_event_subframe_ != new_subframe) {
     last_mouse_move_event_subframe_->GetEventHandler().HandleMouseLeaveEvent(
         mev.Event());
+    last_mouse_move_event_subframe_->GetEventHandler()
+        .mouse_event_manager_->SetLastMousePositionAsUnknown();
   }
 
   if (new_subframe) {
diff --git a/chromium/third_party/WebKit/Source/core/input/MouseEventManager.cpp b/chromium/third_party/WebKit/Source/core/input/MouseEventManager.cpp
index 9ac9bf3478a..607ec9a47e0 100644
--- a/chromium/third_party/WebKit/Source/core/input/MouseEventManager.cpp
+++ b/chromium/third_party/WebKit/Source/core/input/MouseEventManager.cpp
@@ -583,11 +583,15 @@ FloatPoint MouseEventManager::LastKnownMousePositionGlobal() {
 }
 
 void MouseEventManager::SetLastKnownMousePosition(const WebMouseEvent& event) {
-  is_mouse_position_unknown_ = false;
+  is_mouse_position_unknown_ = event.GetType() == WebInputEvent::kMouseLeave;
   last_known_mouse_position_ = event.PositionInRootFrame();
   last_known_mouse_global_position_ = event.PositionInScreen();
 }
 
+void MouseEventManager::SetLastMousePositionAsUnknown() {
+  is_mouse_position_unknown_ = true;
+}
+
 void MouseEventManager::DispatchFakeMouseMoveEventSoon(
     MouseEventManager::FakeMouseMoveReason fake_mouse_move_reason) {
   if (fake_mouse_move_reason ==
diff --git a/chromium/third_party/WebKit/Source/core/input/MouseEventManager.h b/chromium/third_party/WebKit/Source/core/input/MouseEventManager.h
index 02d61cd3ac6..6f56ed44ee7 100644
--- a/chromium/third_party/WebKit/Source/core/input/MouseEventManager.h
+++ b/chromium/third_party/WebKit/Source/core/input/MouseEventManager.h
@@ -93,6 +93,7 @@ class CORE_EXPORT MouseEventManager final
   void DispatchFakeMouseMoveEventSoonInQuad(const FloatQuad&);
 
   void SetLastKnownMousePosition(const WebMouseEvent&);
+  void SetLastMousePositionAsUnknown();
 
   bool HandleDragDropIfPossible(const GestureEventWithHitTestResults&);