Pass accurate contentsScale to LayerImpl.

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 "config.h"
 
 #include "cc/layer_tree_host_impl.h"
 
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
@@ skipping 1084 matching lines @@
     FloatPoint localStartPoint = MathUtil::projectPoint(inverseScreenSpaceTransform, screenSpacePoint, startClipped);
     FloatPoint localEndPoint = MathUtil::projectPoint(inverseScreenSpaceTransform, screenSpaceEndPoint, endClipped);
 
     // In general scroll point coordinates should not get clipped.
     DCHECK(!startClipped);
     DCHECK(!endClipped);
     if (startClipped || endClipped)
         return FloatSize();
 
     // localStartPoint and localEndPoint are in content space but we want to move them to layer space for scrolling.
-    float widthScale = 1;
-    float heightScale = 1;
-    if (!layerImpl.contentBounds().isEmpty() && !layerImpl.bounds().isEmpty()) {
-        widthScale = layerImpl.bounds().width() / static_cast<float>(layerImpl.contentBounds().width());
-        heightScale = layerImpl.bounds().height() / static_cast<float>(layerImpl.contentBounds().height());
-    }
+    float widthScale = 1.0 / layerImpl.contentsScaleX();
+    float heightScale = 1.0 / layerImpl.contentsScaleY();
     localStartPoint.scale(widthScale, heightScale);
     localEndPoint.scale(widthScale, heightScale);
 
     // Apply the scroll delta.
     FloatSize previousDelta(layerImpl.scrollDelta());
     FloatSize unscrolled = layerImpl.scrollBy(localEndPoint - localStartPoint);
 
     if (viewport)
         viewport->applyScroll(unscrolled);
 
@@ skipping 364 matching lines @@
     ScrollbarAnimationController* scrollbarController = layer->scrollbarAnimationController();
     double monotonicTime = (time - base::TimeTicks()).InSecondsF();
     if (scrollbarController && scrollbarController->animate(monotonicTime))
         m_client->setNeedsRedrawOnImplThread();
 
     for (size_t i = 0; i < layer->children().size(); ++i)
         animateScrollbarsRecursive(layer->children()[i], time);
 }
 
 }  // namespace cc