Move use of DisplayItemList's vector behind an explicit DisplayItems interface.

Source/core/paint/LayerClipRecorderTest.cpp

 // Copyright 2014 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 "core/paint/LayerClipRecorder.h"
 
 #include "core/layout/LayoutTestHelper.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/compositing/DeprecatedPaintLayerCompositor.h"
@@ skipping 49 matching lines @@
 
 TEST_F(LayerClipRecorderTest, Single)
 {
     GraphicsContext context(&rootDisplayItemList());
     FloatRect bound = layoutView().viewRect();
     EXPECT_EQ((size_t)0, rootDisplayItemList().displayItems().size());
 
     drawRectInClip(context, layoutView(), PaintPhaseForeground, bound);
     rootDisplayItemList().commitNewDisplayItems();
     EXPECT_EQ((size_t)3, rootDisplayItemList().displayItems().size());
-    EXPECT_TRUE(rootDisplayItemList().displayItems()[0]->isClip());
-    EXPECT_TRUE(rootDisplayItemList().displayItems()[1]->isDrawing());
-    EXPECT_TRUE(rootDisplayItemList().displayItems()[2]->isEndClip());
+    EXPECT_TRUE(DisplayItem::isClipType(rootDisplayItemList().displayItems()[0].type()));
+    EXPECT_TRUE(DisplayItem::isDrawingType(rootDisplayItemList().displayItems()[1].type()));
+    EXPECT_TRUE(DisplayItem::isEndClipType(rootDisplayItemList().displayItems()[2].type()));
 }
 
 TEST_F(LayerClipRecorderTest, Empty)
 {
     GraphicsContext context(&rootDisplayItemList());
     FloatRect bound = layoutView().viewRect();
     EXPECT_EQ((size_t)0, rootDisplayItemList().displayItems().size());
 
     drawEmptyClip(context, layoutView(), PaintPhaseForeground, bound);
     rootDisplayItemList().commitNewDisplayItems();
     EXPECT_EQ((size_t)0, rootDisplayItemList().displayItems().size());
 }
 
 }
 }