Implementation of device metrics emulation in render view.

content/renderer/gpu/render_widget_compositor.h

 // Copyright (c) 2013 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.
 
 #ifndef CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_
 #define CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_
 
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "cc/debug/rendering_stats.h"
@@ skipping 35 matching lines @@
   void GetRenderingStats(cc::RenderingStats* stats);
   void UpdateTopControlsState(cc::TopControlsState constraints,
                               cc::TopControlsState current,
                               bool animate);
   void SetOverdrawBottomHeight(float overdraw_bottom_height);
   void SetNeedsRedrawRect(gfx::Rect damage_rect);
   void SetLatencyInfo(const ui::LatencyInfo& latency_info);
   int GetLayerTreeId() const;
   void NotifyInputThrottledUntilCommit();
   const cc::Layer* GetRootLayer() const;
+  // Pass zero to cancel overriding.
+  void OverrideDeviceScaleFactor(float device_scale);

[aelias_OOO_until_Jul13, 2013/09/13 23:51:44]

Obsolete?

[dgozman, 2013/09/14 07:42:42]

Nope. This is to ensure that compositor has the real deviceScaleFactor instead
of emulated one passed from blink.

[aelias_OOO_until_Jul13, 2013/09/14 07:53:10]

Hmm, in that case I would prefer that your override be made within Blink at the
moment of passing the device_scale_factor to CC, instead of overriding it on the
side here.

[dgozman, 2013/09/19 10:17:11]

Done.

 
   // WebLayerTreeView implementation.
   virtual void setSurfaceReady();
   virtual void setRootLayer(const WebKit::WebLayer& layer);
   virtual void clearRootLayer();
   virtual void setViewportSize(
       const WebKit::WebSize& unused_deprecated,
       const WebKit::WebSize& device_viewport_size);
   virtual WebKit::WebSize layoutViewportSize() const;
   virtual WebKit::WebSize deviceViewportSize() const;
@@ skipping 47 matching lines @@
       OffscreenContextProviderForCompositorThread() OVERRIDE;
 
  private:
   RenderWidgetCompositor(RenderWidget* widget, bool threaded);
 
   bool initialize(cc::LayerTreeSettings settings);
 
   bool threaded_;
   bool suppress_schedule_composite_;
   RenderWidget* widget_;
+  // This stores the original device scale to restore back after device scale
+  // override is canceled. Zero means no override is in place.
+  float saved_device_scale_factor_;
   scoped_ptr<cc::LayerTreeHost> layer_tree_host_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_