Introduce ForwardsTextBuffer and BackwardsTextBuffer

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

Index: third_party/WebKit/Source/core/editing/iterators/ForwardsTextBuffer.h
diff --git a/third_party/WebKit/Source/core/editing/iterators/ForwardsTextBuffer.h b/third_party/WebKit/Source/core/editing/iterators/ForwardsTextBuffer.h
new file mode 100644
index 0000000000000000000000000000000000000000..cb7a581048606f97146e7cdb1c65ee73bc0fdc4f
--- /dev/null
+++ b/third_party/WebKit/Source/core/editing/iterators/ForwardsTextBuffer.h
@@ -0,0 +1,25 @@
+// 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 ForwardsTextBuffer_h
+#define ForwardsTextBuffer_h
+
+#include "core/editing/iterators/TextBufferBase.h"
+
+namespace blink {
+
+class CORE_EXPORT ForwardsTextBuffer final : public TextBufferBase {
+    STACK_ALLOCATED();
+    WTF_MAKE_NONCOPYABLE(ForwardsTextBuffer);
+public:
+    ForwardsTextBuffer() {}
+    const UChar* data() const override;
+
+private:
+    UChar* calcDestination(size_t length) override;
+};
+
+} // namespace blink
+
+#endif // TextBuffer_h