Explicitly specify contents scale for SurfaceLayer.

ui/compositor/layer.cc

 // Copyright (c) 2012 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 "ui/compositor/layer.h"
 
 #include <algorithm>
 
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
@@ skipping 561 matching lines @@
 void Layer::SetShowSurface(
     cc::SurfaceId surface_id,
     const cc::SurfaceLayer::SatisfyCallback& satisfy_callback,
     const cc::SurfaceLayer::RequireCallback& require_callback,
     gfx::Size surface_size,
     gfx::Size frame_size_in_dip) {
   DCHECK(type_ == LAYER_TEXTURED || type_ == LAYER_SOLID_COLOR);
 
   scoped_refptr<cc::SurfaceLayer> new_layer =
       cc::SurfaceLayer::Create(satisfy_callback, require_callback);
-  new_layer->SetSurfaceId(surface_id, surface_size);
+  float scale =
+      frame_size_in_dip.width() > 0
+          ? static_cast<float>(surface_size.width()) / frame_size_in_dip.width()
+          : 1.f;

[piman, 2014/11/12 02:36:57]

Any reason we're not passing the renderer's DSF instead of recomputing it?

In the caller, frame_size_in_dip is computed explicitly from the frame_size
(surface_size) and the renderer's DSF. It seems it would avoid additional
precision issues for non-pow2 DSF.

+  new_layer->SetSurfaceId(surface_id, scale, surface_size);
   SwitchToLayer(new_layer);
   surface_layer_ = new_layer;
 
   frame_size_in_dip_ = frame_size_in_dip;
   RecomputeDrawsContentAndUVRect();
 }
 
 void Layer::SetShowSolidColorContent() {
   DCHECK_EQ(type_, LAYER_SOLID_COLOR);
 
@@ skipping 454 matching lines @@
       children_.end(),
       std::bind2nd(std::mem_fun(&Layer::RemoveAnimatorsInTreeFromCollection),
                    collection));
 }
 
 bool Layer::IsAnimating() const {
   return animator_.get() && animator_->is_animating();
 }
 
 }  // namespace ui