Use the asynchronous version of CopyFromBackingStore in CaptureVisibleTabFunction.

chrome/browser/extensions/extension_tabs_module.h

Index: chrome/browser/extensions/extension_tabs_module.h
diff --git a/chrome/browser/extensions/extension_tabs_module.h b/chrome/browser/extensions/extension_tabs_module.h
index 7738d75be6f4a6554f2fad5d5b5dd0115fed3bd7..085b7437733c31195c734e4eb9918c8069110abf 100644
--- a/chrome/browser/extensions/extension_tabs_module.h
+++ b/chrome/browser/extensions/extension_tabs_module.h
@@ -27,6 +27,9 @@ class DictionaryValue;
 namespace content {
 class WebContents;
 }  // namespace content
+namespace skia {
+class PlatformCanvas;
+}  // namespace skia
 
 // Windows
 class GetWindowFunction : public SyncExtensionFunction {
@@ -181,6 +184,10 @@ class CaptureVisibleTabFunction : public AsyncExtensionFunction,
                        const content::NotificationDetails& details) OVERRIDE;
   void SendResultFromBitmap(const SkBitmap& screen_capture);
 
+ private:
+  void CopyFromBackingStoreComplete(skia::PlatformCanvas* canvas,
+                                    bool succeeded);
+
   content::NotificationRegistrar registrar_;
 
   // The format (JPEG vs PNG) of the resulting image.  Set in RunImpl().