Introduce ForwardsTextBuffer and BackwardsTextBuffer

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

Index: third_party/WebKit/Source/core/editing/iterators/TextBufferBase.cpp
diff --git a/third_party/WebKit/Source/core/editing/iterators/TextBufferBase.cpp b/third_party/WebKit/Source/core/editing/iterators/TextBufferBase.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..2a79a5c97c82a579c2a998dc21687b3ed7438e9e
--- /dev/null
+++ b/third_party/WebKit/Source/core/editing/iterators/TextBufferBase.cpp
@@ -0,0 +1,42 @@
+// 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.
+
+#include "core/editing/iterators/TextBufferBase.h"
+
+namespace blink {
+
+TextBufferBase::TextBufferBase()
+{
+    m_buffer.resize(capacity());
+}
+
+void TextBufferBase::shiftData(size_t)
+{
+}
+
+void TextBufferBase::pushCharacters(UChar ch, size_t length)
+{
+    if (length == 0)
+        return;
+    std::fill_n(ensureDestination(length), length, ch);
+}
+
+UChar* TextBufferBase::ensureDestination(size_t length)
+{
+    if (m_size + length > capacity())
+        grow(m_size + length);
+    UChar* ans = calcDestination(length);
+    m_size += length;
+    return ans;
+}
+
+void TextBufferBase::grow(size_t demand)
+{
+    size_t oldCapacity = capacity();
+    m_buffer.resize(demand);
+    m_buffer.resize(capacity());
+    shiftData(oldCapacity);
+}
+
+} // namespace blink