Implement "Save image as" for canvas (chromium side).

content/browser/renderer_host/render_view_host_impl.h

Index: content/browser/renderer_host/render_view_host_impl.h
diff --git a/content/browser/renderer_host/render_view_host_impl.h b/content/browser/renderer_host/render_view_host_impl.h
index 276bdf4c19d4d329675410b0e741bb750ec84662..51694a27788b6e6759cdc07581b8f7c8612c9495 100644
--- a/content/browser/renderer_host/render_view_host_impl.h
+++ b/content/browser/renderer_host/render_view_host_impl.h
@@ -157,6 +157,7 @@ class CONTENT_EXPORT RenderViewHostImpl
   virtual void ClearFocusedElement() OVERRIDE;
   virtual void ClosePage() OVERRIDE;
   virtual void CopyImageAt(int x, int y) OVERRIDE;
+  virtual void SaveImageAt(int x, int y) OVERRIDE;
   virtual void DirectoryEnumerationFinished(
       int request_id,
       const std::vector<base::FilePath>& files) OVERRIDE;