Introduce XGetImage() for GrabWindowSnapshot() in ChromeOS.

ui/aura/root_window.h

Index: ui/aura/root_window.h
diff --git a/ui/aura/root_window.h b/ui/aura/root_window.h
index 53ffab5e596286be167734d131528d5a5dc39891..ae90f549f6ad93ea022c9aaa9beca0091bbdbe3d 100644
--- a/ui/aura/root_window.h
+++ b/ui/aura/root_window.h
@@ -6,6 +6,8 @@
 #define UI_AURA_ROOT_WINDOW_H_
 #pragma once
 
+#include <vector>
+
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ -241,6 +243,10 @@ class AURA_EXPORT RootWindow : public ui::CompositorDelegate,
   // Sets if the window should be focused when shown.
   void SetFocusWhenShown(bool focus_when_shown);
 
+  // Grabs the snapshot of the root window by using the platform-dependent APIs.
+  bool GrabSnapshot(const gfx::Rect& snapshot_bounds,
+                    std::vector<unsigned char>* png_representation);
+
   // Overridden from Window:
   virtual RootWindow* GetRootWindow() OVERRIDE;
   virtual const RootWindow* GetRootWindow() const OVERRIDE;