Made root translation layer the root when using pinch virtual viewport.

Source/core/frame/PinchViewport.cpp

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 177 matching lines @@
     setLocation(visibleRect().location());
 
     // TODO: We should probably be calling scaleDidChange type functions here.
     // see Page::setPageScaleFactor.
 }
 
 // Modifies the top of the graphics layer tree to add layers needed to support
 // the inner/outer viewport fixed-position model for pinch zoom. When finished,
 // the tree will look like this (with * denoting added layers):
 //
-// *innerViewportContainerLayer (fixed pos container)
-//  +- *pageScaleLayer
-//  |   +- *innerViewportScrollLayer
-//  |       +-- overflowControlsHostLayer (root layer)
-//  |           +-- rootTransformLayer (optional)
+// *rootTransformLayer
+//  +- *innerViewportContainerLayer (fixed pos container)
+//      +- *pageScaleLayer
+//  |       +- *innerViewportScrollLayer
+//  |           +-- overflowControlsHostLayer (root layer)
 //  |               +-- outerViewportContainerLayer (fixed pos container) [frame container layer in RenderLayerCompositor]
 //  |               |   +-- outerViewportScrollLayer [frame scroll layer in RenderLayerCompositor]
 //  |               |       +-- content layers ...
 //  |               +-- horizontal ScrollbarLayer (non-overlay)
 //  |               +-- verticalScrollbarLayer (non-overlay)
 //  |               +-- scroll corner (non-overlay)
 //  +- *horizontalScrollbarLayer (overlay)
 //  +- *verticalScrollbarLayer (overlay)
 //
 void PinchViewport::attachToLayerTree(GraphicsLayer* currentLayerTreeRoot, GraphicsLayerFactory* graphicsLayerFactory)
 {
     TRACE_EVENT1("webkit", "PinchViewport::attachToLayerTree", "currentLayerTreeRoot", (bool)currentLayerTreeRoot);
     if (!currentLayerTreeRoot) {
         m_innerViewportScrollLayer->removeAllChildren();
         return;
     }
 
     if (currentLayerTreeRoot->parent() && currentLayerTreeRoot->parent() == m_innerViewportScrollLayer)
         return;
 
     if (!m_innerViewportScrollLayer) {
         ASSERT(!m_overlayScrollbarHorizontal
             && !m_overlayScrollbarVertical
             && !m_pageScaleLayer
             && !m_innerViewportContainerLayer);
 
+        // FIXME: The root transform layer should only be created on demand.
+        m_rootTransformLayer = GraphicsLayer::create(graphicsLayerFactory, this);
         m_innerViewportContainerLayer = GraphicsLayer::create(graphicsLayerFactory, this);
         m_pageScaleLayer = GraphicsLayer::create(graphicsLayerFactory, this);
         m_innerViewportScrollLayer = GraphicsLayer::create(graphicsLayerFactory, this);
         m_overlayScrollbarHorizontal = GraphicsLayer::create(graphicsLayerFactory, this);
         m_overlayScrollbarVertical = GraphicsLayer::create(graphicsLayerFactory, this);
 
         WebCore::ScrollingCoordinator* coordinator = m_frameHost.page().scrollingCoordinator();
         ASSERT(coordinator);
         coordinator->setLayerIsContainerForFixedPositionLayers(m_innerViewportScrollLayer.get(), true);
 
         // Set masks to bounds so the compositor doesn't clobber a manually
         // set inner viewport container layer size.
         m_innerViewportContainerLayer->setMasksToBounds(m_frameHost.settings().mainFrameClipsContent());
         m_innerViewportContainerLayer->setSize(m_size);
 
         m_innerViewportScrollLayer->platformLayer()->setScrollClipLayer(
             m_innerViewportContainerLayer->platformLayer());
         m_innerViewportScrollLayer->platformLayer()->setUserScrollable(true, true);
 
+        m_rootTransformLayer->addChild(m_innerViewportContainerLayer.get());
         m_innerViewportContainerLayer->addChild(m_pageScaleLayer.get());
         m_pageScaleLayer->addChild(m_innerViewportScrollLayer.get());
         m_innerViewportContainerLayer->addChild(m_overlayScrollbarHorizontal.get());
         m_innerViewportContainerLayer->addChild(m_overlayScrollbarVertical.get());
 
         // Ensure this class is set as the scroll layer's ScrollableArea.
         coordinator->scrollableAreaScrollLayerDidChange(this);
 
         // Setup the inner viewport overlay scrollbars.
         setupScrollbar(WebScrollbar::Horizontal);
@@ skipping 182 matching lines @@
     } else if (graphicsLayer == m_overlayScrollbarVertical.get()) {
         name =  "Overlay Scrollbar Vertical Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore