Put transform tree building in DisplayItemPropertyTreeBuilder.

Source/platform/graphics/paint/DisplayItemClipTree.cpp

Index: Source/platform/graphics/paint/DisplayItemClipTree.cpp
diff --git a/Source/platform/graphics/paint/DisplayItemClipTree.cpp b/Source/platform/graphics/paint/DisplayItemClipTree.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..6e7ddb840b9e5308f42c91486450eb1ff9f4c7ff
--- /dev/null
+++ b/Source/platform/graphics/paint/DisplayItemClipTree.cpp
@@ -0,0 +1,26 @@
+// 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 "platform/graphics/paint/DisplayItemClipTree.h"
+
+#include <limits>
+
+namespace blink {
+
+DisplayItemClipTree::DisplayItemClipTree()
+{
+    // There is always a root node.
+    // And it's always in the root transform space.
+    float infinity = std::numeric_limits<float>::infinity();
+    WebFloatRect infiniteRect(-infinity, -infinity, infinity, infinity);

[pdr., 2015/08/17 22:25:07]

add WebFloatRect::infiniteRect()?

+    m_nodes.append(ClipNode(kInvalidIndex, 0 /* root transform node */, infiniteRect));
+    ASSERT(m_nodes[0].isRoot());
+}
+
+DisplayItemClipTree::~DisplayItemClipTree()
+{
+}
+
+} // namespace blink