Align physical pixels of scrolled layers

cc/layer_tree_host_impl.cc

 // Copyright 2011 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 "cc/layer_tree_host_impl.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
@@ skipping 901 matching lines @@
 LayerImpl* LayerTreeHostImpl::rootScrollLayer() const
 {
   return m_activeTree->RootScrollLayer();
 }
 
 LayerImpl* LayerTreeHostImpl::currentlyScrollingLayer() const
 {
   return m_activeTree->CurrentlyScrollingLayer();
 }
 
-// Content layers can be either directly scrollable or contained in an outer
-// scrolling layer which applies the scroll transform. Given a content layer,
-// this function returns the associated scroll layer if any.
-static LayerImpl* findScrollLayerForContentLayer(LayerImpl* layerImpl)
-{
-    if (!layerImpl)
-        return 0;
-
-    if (layerImpl->scrollable())
-        return layerImpl;
-
-    if (layerImpl->drawsContent() && layerImpl->parent() && layerImpl->parent()->scrollable())
-        return layerImpl->parent();
-
-    return 0;
-}
-
 void LayerTreeHostImpl::createPendingTree()
 {
     CHECK(!m_pendingTree);
     if (m_recycleTree)
         m_recycleTree.swap(m_pendingTree);
     else
         m_pendingTree = LayerTreeImpl::create(this);
     m_client->onCanDrawStateChanged(canDraw());
     m_client->onHasPendingTreeStateChanged(pendingTree());
     TRACE_EVENT_ASYNC_BEGIN0("cc", "PendingTree", m_pendingTree.get());
@@ skipping 244 matching lines @@
     // Walk up the hierarchy and look for a scrollable layer.
     LayerImpl* potentiallyScrollingLayerImpl = 0;
     for (; layerImpl; layerImpl = layerImpl->parent()) {
         // The content layer can also block attempts to scroll outside the main thread.
         if (layerImpl->tryScroll(deviceViewportPoint, type) == ScrollOnMainThread) {
             m_numMainThreadScrolls++;
             UMA_HISTOGRAM_BOOLEAN("TryScroll.SlowScroll", true);
             return ScrollOnMainThread;
         }
 
-        LayerImpl* scrollLayerImpl = findScrollLayerForContentLayer(layerImpl);
+        LayerImpl* scrollLayerImpl = LayerTreeHostCommon::findScrollLayerForContentLayer(layerImpl);
         if (!scrollLayerImpl)
             continue;
 
         ScrollStatus status = scrollLayerImpl->tryScroll(deviceViewportPoint, type);
 
         // If any layer wants to divert the scroll event to the main thread, abort.
         if (status == ScrollOnMainThread) {
             m_numMainThreadScrolls++;
             UMA_HISTOGRAM_BOOLEAN("TryScroll.SlowScroll", true);
             return ScrollOnMainThread;
@@ skipping 510 matching lines @@
         m_tileManager->SetRecordRenderingStats(m_debugState.recordRenderingStats());
 }
 
 void LayerTreeHostImpl::savePaintTime(const base::TimeDelta& totalPaintTime, int commitNumber)
 {
     DCHECK(m_debugState.continuousPainting);
     m_paintTimeCounter->SavePaintTime(totalPaintTime, commitNumber);
 }
 
 }  // namespace cc