Share backing canvases between browser compositors.

content/browser/compositor/software_output_device_win.h

Index: content/browser/compositor/software_output_device_win.h
diff --git a/content/browser/compositor/software_output_device_win.h b/content/browser/compositor/software_output_device_win.h
index 7063f207b00cfa446e5979cad1671c91bb465c9a..8b7fc160dc3cc182417dad56fae5aa6668009da0 100644
--- a/content/browser/compositor/software_output_device_win.h
+++ b/content/browser/compositor/software_output_device_win.h
@@ -5,13 +5,15 @@
 #ifndef CONTENT_BROWSER_COMPOSITOR_SOFTWARE_OUTPUT_DEVICE_WIN_H_
 #define CONTENT_BROWSER_COMPOSITOR_SOFTWARE_OUTPUT_DEVICE_WIN_H_
 
+#include <vector>
+
 #include "base/memory/scoped_ptr.h"
 #include "cc/output/software_output_device.h"
 
 #include <windows.h>
 
-namespace gfx {
-class Canvas;
+namespace base {
+class SharedMemory;
 }
 
 namespace ui {
@@ -19,10 +21,32 @@ class Compositor;
 }
 
 namespace content {
+class SoftwareOutputDeviceWin;
+
+class OutputDeviceBacking {
+ public:
+  OutputDeviceBacking();
+  ~OutputDeviceBacking();
+
+  void Resized();
+  void RegisterOutputDevice(SoftwareOutputDeviceWin* device);
+  void UnregisterOutputDevice(SoftwareOutputDeviceWin* device);
+  base::SharedMemory* GetSharedMemory();
+
+ private:
+  size_t GetMaxByteSize();
+
+  std::vector<SoftwareOutputDeviceWin*> devices_;
+  scoped_ptr<base::SharedMemory> backing_;
+  size_t created_byte_size_;
+
+  DISALLOW_COPY_AND_ASSIGN(OutputDeviceBacking);
+};
 
 class SoftwareOutputDeviceWin : public cc::SoftwareOutputDevice {
  public:
-  explicit SoftwareOutputDeviceWin(ui::Compositor* compositor);
+  SoftwareOutputDeviceWin(OutputDeviceBacking* backing,
+                          ui::Compositor* compositor);
   ~SoftwareOutputDeviceWin() override;
 
   void Resize(const gfx::Size& viewport_pixel_size,
@@ -30,11 +54,15 @@ class SoftwareOutputDeviceWin : public cc::SoftwareOutputDevice {
   SkCanvas* BeginPaint(const gfx::Rect& damage_rect) override;
   void EndPaint(cc::SoftwareFrameData* frame_data) override;
 
+  gfx::Size viewport_pixel_size() const { return viewport_pixel_size_; }
+  void ReleaseContents();
+
  private:
   HWND hwnd_;
-  BITMAPINFO bitmap_info_;
-  scoped_ptr<gfx::Canvas> contents_;
+  skia::RefPtr<SkCanvas> contents_;
   bool is_hwnd_composited_;
+  OutputDeviceBacking* backing_;
+  bool in_paint_;
 
   DISALLOW_COPY_AND_ASSIGN(SoftwareOutputDeviceWin);
 };