Set the scrollbarLayer as opaque after setupScrollbarLayer.

Source/web/tests/ScrollingCoordinatorChromiumTest.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 88 matching lines @@
     static void configureSettings(WebSettings* settings)
     {
         settings->setJavaScriptEnabled(true);
         settings->setAcceleratedCompositingEnabled(true);
         settings->setPreferCompositingToLCDTextEnabled(true);
     }
 
     FrameTestHelpers::WebViewHelper m_helper;
 };
 
+class GraphicsLayerForScrollTesting : public GraphicsLayer {
+public:
+    virtual WebLayer* contentsLayer() const { return GraphicsLayer::contentsLayer(); }
+};
+
 TEST_F(ScrollingCoordinatorChromiumTest, fastScrollingByDefault)
 {
     navigateTo("about:blank");
     forceFullCompositingUpdate();
 
     // Make sure the scrolling coordinator is active.
     FrameView* frameView = frame()->view();
     Page* page = frame()->page();
     ASSERT_TRUE(page->scrollingCoordinator());
     ASSERT_TRUE(page->scrollingCoordinator()->coordinatesScrollingForFrameView(frameView));
@@ skipping 348 matching lines @@
 
 TEST_F(ScrollingCoordinatorChromiumTest, setupScrollbarLayerShouldNotCrash)
 {
     registerMockedHttpURLLoad("setup_scrollbar_layer_crash.html");
     navigateTo(m_baseURL + "setup_scrollbar_layer_crash.html");
     forceFullCompositingUpdate();
     // This test document setup an iframe with scrollbars, then switch to
     // an empty document by javascript.
 }
 
+TEST_F(ScrollingCoordinatorChromiumTest, setupScrollbarLayerShouldSetScrollLayerOpaque)
+{
+    registerMockedHttpURLLoad("wide_document.html");
+    navigateTo(m_baseURL + "wide_document.html");
+    forceFullCompositingUpdate();
+
+    FrameView* frameView = frame()->view();
+    ASSERT_TRUE(frameView);
+
+    GraphicsLayerForScrollTesting* scrollbarGraphicsLayer = static_cast<GraphicsLayerForScrollTesting*>(frameView->layerForHorizontalScrollbar());
+    ASSERT_TRUE(scrollbarGraphicsLayer);
+
+    WebLayer* platformLayer = scrollbarGraphicsLayer->platformLayer();
+    ASSERT_TRUE(platformLayer);
+
+    WebLayer* contentsLayer = scrollbarGraphicsLayer->contentsLayer();
+    ASSERT_TRUE(contentsLayer);
+
+    // after scrollableAreaScrollbarLayerDidChange,

[enne (OOO), 2014/10/13 21:34:00]

Tiny nit: capitalize the 'A' in 'After', since it's starting a sentence.

+    // if the main frame's scrollbarLayer is opaque,
+    // contentsLayer should be opaque too.
+    ASSERT_EQ(platformLayer->opaque(), contentsLayer->opaque());
+}
+
 } // namespace