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diff --git a/Source/WTF/wtf/text/TextBreakIterator.h b/Source/WTF/wtf/text/TextBreakIterator.h
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+++ b/Source/WTF/wtf/text/TextBreakIterator.h
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+/*
+ * Copyright (C) 2006 Lars Knoll <lars@trolltech.com>
+ * Copyright (C) 2007-2016 Apple Inc. All rights reserved.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public License
+ * along with this library; see the file COPYING.LIB.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ *
+ */
+
+#pragma once
+
+#include <wtf/text/StringView.h>
+
+namespace WTF {
+
+// Note: The returned iterator is good only until you get another iterator, with the exception of acquireLineBreakIterator.
+
+enum class LineBreakIteratorMode { Default, Loose, Normal, Strict };
+
+// This is similar to character break iterator in most cases, but is subject to
+// platform UI conventions. One notable example where this can be different
+// from character break iterator is Thai prepend characters, see bug 24342.
+// Use this for insertion point and selection manipulations.
+WTF_EXPORT_PRIVATE UBreakIterator* cursorMovementIterator(StringView);
+
+WTF_EXPORT_PRIVATE UBreakIterator* wordBreakIterator(StringView);
+WTF_EXPORT_PRIVATE UBreakIterator* sentenceBreakIterator(StringView);
+
+WTF_EXPORT_PRIVATE UBreakIterator* acquireLineBreakIterator(StringView, const AtomicString& locale, const UChar* priorContext, unsigned priorContextLength, LineBreakIteratorMode);
+WTF_EXPORT_PRIVATE void releaseLineBreakIterator(UBreakIterator*);
+UBreakIterator* openLineBreakIterator(const AtomicString& locale);
+void closeLineBreakIterator(UBreakIterator*&);
+
+WTF_EXPORT_PRIVATE bool isWordTextBreak(UBreakIterator*);
+
+class LazyLineBreakIterator {
+public:
+    LazyLineBreakIterator()
+    {
+        resetPriorContext();
+    }
+
+    explicit LazyLineBreakIterator(StringView stringView, const AtomicString& locale = AtomicString(), LineBreakIteratorMode mode = LineBreakIteratorMode::Default)
+        : m_stringView(stringView)
+        , m_locale(locale)
+        , m_mode(mode)
+    {
+        resetPriorContext();
+    }
+
+    ~LazyLineBreakIterator()
+    {
+        if (m_iterator)
+            releaseLineBreakIterator(m_iterator);
+    }
+
+    StringView stringView() const { return m_stringView; }
+    LineBreakIteratorMode mode() const { return m_mode; }
+
+    UChar lastCharacter() const
+    {
+        static_assert(WTF_ARRAY_LENGTH(m_priorContext) == 2, "UBreakIterator unexpected prior context length");
+        return m_priorContext[1];
+    }
+
+    UChar secondToLastCharacter() const
+    {
+        static_assert(WTF_ARRAY_LENGTH(m_priorContext) == 2, "UBreakIterator unexpected prior context length");
+        return m_priorContext[0];
+    }
+
+    void setPriorContext(UChar last, UChar secondToLast)
+    {
+        static_assert(WTF_ARRAY_LENGTH(m_priorContext) == 2, "UBreakIterator unexpected prior context length");
+        m_priorContext[0] = secondToLast;
+        m_priorContext[1] = last;
+    }
+
+    void updatePriorContext(UChar last)
+    {
+        static_assert(WTF_ARRAY_LENGTH(m_priorContext) == 2, "UBreakIterator unexpected prior context length");
+        m_priorContext[0] = m_priorContext[1];
+        m_priorContext[1] = last;
+    }
+
+    void resetPriorContext()
+    {
+        static_assert(WTF_ARRAY_LENGTH(m_priorContext) == 2, "UBreakIterator unexpected prior context length");
+        m_priorContext[0] = 0;
+        m_priorContext[1] = 0;
+    }
+
+    unsigned priorContextLength() const
+    {
+        unsigned priorContextLength = 0;
+        static_assert(WTF_ARRAY_LENGTH(m_priorContext) == 2, "UBreakIterator unexpected prior context length");
+        if (m_priorContext[1]) {
+            ++priorContextLength;
+            if (m_priorContext[0])
+                ++priorContextLength;
+        }
+        return priorContextLength;
+    }
+
+    // Obtain text break iterator, possibly previously cached, where this iterator is (or has been)
+    // initialized to use the previously stored string as the primary breaking context and using
+    // previously stored prior context if non-empty.
+    UBreakIterator* get(unsigned priorContextLength)
+    {
+        ASSERT(priorContextLength <= priorContextCapacity);
+        const UChar* priorContext = priorContextLength ? &m_priorContext[priorContextCapacity - priorContextLength] : 0;
+        if (!m_iterator) {
+            m_iterator = acquireLineBreakIterator(m_stringView, m_locale, priorContext, priorContextLength, m_mode);
+            m_cachedPriorContext = priorContext;
+            m_cachedPriorContextLength = priorContextLength;
+        } else if (priorContext != m_cachedPriorContext || priorContextLength != m_cachedPriorContextLength) {
+            resetStringAndReleaseIterator(m_stringView, m_locale, m_mode);
+            return this->get(priorContextLength);
+        }
+        return m_iterator;
+    }
+
+    void resetStringAndReleaseIterator(StringView stringView, const AtomicString& locale, LineBreakIteratorMode mode)
+    {
+        if (m_iterator)
+            releaseLineBreakIterator(m_iterator);
+        m_stringView = stringView;
+        m_locale = locale;
+        m_iterator = nullptr;
+        m_cachedPriorContext = nullptr;
+        m_mode = mode;
+        m_cachedPriorContextLength = 0;
+    }
+
+private:
+    static constexpr unsigned priorContextCapacity = 2;
+    StringView m_stringView;
+    AtomicString m_locale;
+    UBreakIterator* m_iterator { nullptr };
+    const UChar* m_cachedPriorContext { nullptr };
+    LineBreakIteratorMode m_mode { LineBreakIteratorMode::Default };
+    unsigned m_cachedPriorContextLength { 0 };
+    UChar m_priorContext[priorContextCapacity];
+};
+
+// Iterates over "extended grapheme clusters", as defined in UAX #29.
+// Note that platform implementations may be less sophisticated - e.g. ICU prior to
+// version 4.0 only supports "legacy grapheme clusters".
+// Use this for general text processing, e.g. string truncation.
+
+class NonSharedCharacterBreakIterator {
+    WTF_MAKE_NONCOPYABLE(NonSharedCharacterBreakIterator);
+public:
+    WTF_EXPORT_PRIVATE NonSharedCharacterBreakIterator(StringView);
+    WTF_EXPORT_PRIVATE ~NonSharedCharacterBreakIterator();
+
+    NonSharedCharacterBreakIterator(NonSharedCharacterBreakIterator&&);
+
+    operator UBreakIterator*() const { return m_iterator; }
+
+private:
+    UBreakIterator* m_iterator;
+};
+
+// Counts the number of grapheme clusters. A surrogate pair or a sequence
+// of a non-combining character and following combining characters is
+// counted as 1 grapheme cluster.
+WTF_EXPORT_PRIVATE unsigned numGraphemeClusters(StringView);
+
+// Returns the number of characters which will be less than or equal to
+// the specified grapheme cluster length.
+WTF_EXPORT_PRIVATE unsigned numCharactersInGraphemeClusters(StringView, unsigned);
+
+}
+
+using WTF::LazyLineBreakIterator;
+using WTF::LineBreakIteratorMode;
+using WTF::NonSharedCharacterBreakIterator;
+using WTF::isWordTextBreak;