[cc] Apply sublayer transform about anchor instead of about layer center.

cc/layer_tree_host_common.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_common.h"
 
 #include <algorithm>
 
 #include "base/debug/trace_event.h"
 #include "cc/layer.h"
@@ skipping 849 matching lines @@
             clipRectForSubtree = clipRectFromAncestor;
             clipRectForSubtree.Intersect(rectInTargetSpace);
         } else
             clipRectForSubtree = rectInTargetSpace;
     }
 
     // Flatten to 2D if the layer doesn't preserve 3D.
     if (!layer->preserves3D())
         sublayerMatrix.FlattenTo2d();
 
     // Apply the sublayer transform at the center of the layer.

[danakj, 2013/02/12 00:58:23]

This comment is wrong now.

     if (!layer->sublayerTransform().IsIdentity()) {
-        sublayerMatrix.Translate(0.5 * bounds.width(), 0.5 * bounds.height());
+        sublayerMatrix.Translate(layer->anchorPoint().x() * bounds.width(), layer->anchorPoint().y() * bounds.height());
         sublayerMatrix.PreconcatTransform(layer->sublayerTransform());
-        sublayerMatrix.Translate(-0.5 * bounds.width(), -0.5 * bounds.height());
+        sublayerMatrix.Translate(-layer->anchorPoint().x() * bounds.width(), -layer->anchorPoint().y() * bounds.height());
     }
 
     LayerList& descendants = (layer->renderSurface() ? layer->renderSurface()->layerList() : layerList);
 
     // Any layers that are appended after this point are in the layer's subtree and should be included in the sorting process.
     unsigned sortingStartIndex = descendants.size();
 
     if (!layerShouldBeSkipped(layer))
         descendants.push_back(layer);
 
@@ skipping 313 matching lines @@
 
   // At this point, we think the point does hit the touch event handler region on the layer, but we need to walk up
   // the parents to ensure that the layer was not clipped in such a way that the
   // hit point actually should not hit the layer.
   if (pointIsClippedBySurfaceOrClipRect(screenSpacePoint, layerImpl))
      return false;
 
   return true;
 }
 }  // namespace cc