Add a setting to disable threaded scrolling

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 106 matching lines @@
     ASSERT_TRUE(page->scrollingCoordinator());
     ASSERT_TRUE(page->scrollingCoordinator()->coordinatesScrollingForFrameView(frameView));
 
     // Fast scrolling should be enabled by default.
     WebLayer* rootScrollLayer = getRootScrollLayer();
     ASSERT_TRUE(rootScrollLayer->scrollable());
     ASSERT_FALSE(rootScrollLayer->shouldScrollOnMainThread());
     ASSERT_FALSE(rootScrollLayer->haveWheelEventHandlers());
 }
 
+TEST_F(ScrollingCoordinatorChromiumTest, fastScrollingCanBeDisabledWithSetting)
+{
+    navigateTo("about:blank");
+    webViewImpl()->settings()->setThreadedScrollingEnabled(false);
+    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));
+
+    // Main scrolling should be enabled with the setting override.
+    WebLayer* rootScrollLayer = getRootScrollLayer();
+    ASSERT_TRUE(rootScrollLayer->scrollable());
+    ASSERT_TRUE(rootScrollLayer->shouldScrollOnMainThread());
+}
+
 static WebLayer* webLayerFromElement(Element* element)
 {
     if (!element)
         return 0;
     RenderObject* renderer = element->renderer();
     if (!renderer || !renderer->isBoxModelObject())
         return 0;
     RenderLayer* layer = toRenderBoxModelObject(renderer)->layer();
     if (!layer)
         return 0;
@@ skipping 313 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.
 }
 
 } // namespace