Put transform tree building in DisplayItemPropertyTreeBuilder.

Source/platform/exported/WebDisplayItemClipTree.cpp

Index: Source/platform/exported/WebDisplayItemClipTree.cpp
diff --git a/Source/platform/exported/WebDisplayItemClipTree.cpp b/Source/platform/exported/WebDisplayItemClipTree.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..8625e18a4a39c5fae5a15312c229b68d8adf27b1
--- /dev/null
+++ b/Source/platform/exported/WebDisplayItemClipTree.cpp
@@ -0,0 +1,37 @@
+// Copyright 2015 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 "config.h"
+#include "public/platform/WebDisplayItemClipTree.h"
+
+#include "platform/graphics/paint/DisplayItemClipTree.h"
+
+namespace blink {
+
+WebDisplayItemClipTree::WebDisplayItemClipTree()
+{
+}
+
+WebDisplayItemClipTree::WebDisplayItemClipTree(const PassOwnPtr<DisplayItemClipTree>& passImpl)
+    : m_private(passImpl)
+{
+}
+
+WebDisplayItemClipTree::~WebDisplayItemClipTree()
+{
+    // WebPrivateOwnPtr requires explicit clearing here.
+    m_private.reset(nullptr);
+}
+
+size_t WebDisplayItemClipTree::nodeCount() const
+{
+    return m_private->nodeCount();
+}
+
+const WebDisplayItemClipTree::ClipNode& WebDisplayItemClipTree::nodeAt(size_t index) const
+{
+    return m_private->nodeAt(index);
+}
+
+} // namespace blink