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 34 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();
 
+  // Pass zero to cancel overriding.
+  void OverrideDeviceScaleFactor(float device_scale);
+
   // 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;
   virtual WebKit::WebFloatPoint adjustEventPointForPinchZoom(
@@ skipping 46 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. When device scale if not overriden, this is zero.
+  float saved_device_scale_factor_;
   scoped_ptr<cc::LayerTreeHost> layer_tree_host_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_H_