Introduce ForwardsTextBuffer and BackwardsTextBuffer

third_party/WebKit/Source/core/editing/iterators/TextBufferBase.h

Index: third_party/WebKit/Source/core/editing/iterators/TextBufferBase.h
diff --git a/third_party/WebKit/Source/core/editing/iterators/TextBufferBase.h b/third_party/WebKit/Source/core/editing/iterators/TextBufferBase.h
new file mode 100644
index 0000000000000000000000000000000000000000..27f3be0fd5ba9145ffdbbcaa37a14a2409b5ffcc
--- /dev/null
+++ b/third_party/WebKit/Source/core/editing/iterators/TextBufferBase.h
@@ -0,0 +1,55 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef TextBufferBase_h
+#define TextBufferBase_h
+
+#include "core/CoreExport.h"
+#include "wtf/Vector.h"
+#include "wtf/text/WTFString.h"
+
+namespace blink {
+
+class CORE_EXPORT TextBufferBase {
+    STACK_ALLOCATED();
+    WTF_MAKE_NONCOPYABLE(TextBufferBase);
+public:
+    void clear() { m_size = 0; }
+    size_t size() const { return m_size; }
+    bool isEmpty() const { return m_size == 0; }
+    const UChar& operator[](size_t index) const { ASSERT(index < m_size); return data()[index]; }
+    virtual const UChar* data() const = 0;
+
+    void pushCharacters(UChar, size_t length);
+
+    template<typename T>
+    void pushRange(const T* other, size_t length)
+    {
+        if (length == 0)
+            return;
+        std::copy(other, other + length, ensureDestination(length));
+    }
+
+protected:
+    TextBufferBase();
+    UChar* ensureDestination(size_t length);
+    void grow(size_t demand);
+
+    virtual UChar* calcDestination(size_t length) = 0;
+    virtual void shiftData(size_t oldCapacity);
+
+    size_t capacity() const { return m_buffer.capacity(); }
+    const UChar* bufferBegin() const { return m_buffer.begin(); }
+    const UChar* bufferEnd() const { return m_buffer.end(); }
+    UChar* bufferBegin() { return m_buffer.begin(); }
+    UChar* bufferEnd() { return m_buffer.end(); }
+
+private:
+    size_t m_size = 0;
+    Vector<UChar, 1024> m_buffer;
+};
+
+} // namespace blink
+
+#endif // TextBufferBase_h