[Layout API] Introduce Layout API shim and use in LayerClipRecorderTest.cpp

There are a few final obstacles to removing Document::layoutView() and
FrameView::layoutView(), and they require the use of a shim to bust
through the block layout API. In LayerClipRecorderTest, it gets a
reference to the document's layout view and later passes it to
LayoutObjectDrawingRecorder::useCachedDrawingIfPossible, which in turn
passes it to DrawingRecorder::useCachedDrawingIfPossible, which is
defined in platform/ and can not have a hard dependency on the block
layout API.

BUG=499321

Review-Url: https://codereview.chromium.org/2036213002
Cr-Commit-Position: refs/heads/master@{#397789}

third_party/WebKit/Source/core/core.gypi

@@ -501,6 +501,7 @@
         ],
         'webcore_rendering_files': [
             'layout/api/HitTestAction.h',
+            'layout/api/LayoutAPIShim.h',
             'layout/api/LayoutBlockItem.h',
             'layout/api/LayoutBoxItem.h',
             'layout/api/LayoutBoxModel.h',

third_party/WebKit/Source/core/layout/api/LayoutAPIShim.h

+// 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.
+
+#ifndef LayoutAPIShim_h
+#define LayoutAPIShim_h
+
+#include "core/layout/api/LayoutItem.h"
+
+namespace blink {
+
+class LayoutObject;
+
+// TODO(pilgrim): Remove this kludge once clients have a real API and no longer need access to the underlying LayoutObject.
+class LayoutAPIShim {
+public:
+    static LayoutObject* layoutObjectFrom(LayoutItem item)
+    {
+        return item.layoutObject();
+    }
+
+    static const LayoutObject* constLayoutObjectFrom(LayoutItem item)
+    {
+        return item.layoutObject();
+    }
+};
+
+} // namespace blink
+
+#endif // LayoutAPIShim_h

third_party/WebKit/Source/core/layout/api/LayoutItem.h

@@ -13,6 +13,7 @@
 namespace blink {
 
 class FrameView;
+class LayoutAPIShim;
 class Node;
 
 class LayoutItem {
@@ -257,6 +258,8 @@ protected:
 
 private:
     LayoutObject* m_layoutObject;
+
+    friend class LayoutAPIShim;
 };
 
 } // namespace blink

third_party/WebKit/Source/core/paint/LayerClipRecorderTest.cpp

@@ -6,6 +6,7 @@
 
 #include "core/layout/LayoutTestHelper.h"
 #include "core/layout/LayoutView.h"
+#include "core/layout/api/LayoutAPIShim.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/paint/LayoutObjectDrawingRecorder.h"
 #include "core/paint/PaintLayer.h"
@@ -32,7 +33,7 @@ private:
         RenderingTest::SetUp();
         enableCompositing();
 
-        m_layoutView = document().view()->layoutView();
+        m_layoutView = toLayoutView(LayoutAPIShim::layoutObjectFrom(document().view()->layoutViewItem()));
         ASSERT_TRUE(m_layoutView);
     }