Automated test for dragging between same-page, cross-site frames.

content/public/test/browser_test_utils.h

Index: content/public/test/browser_test_utils.h
diff --git a/content/public/test/browser_test_utils.h b/content/public/test/browser_test_utils.h
index 1deed61f1a9da8609bcd14c7adafa8302b917112..e39416c789bd79e3bded26d7690201a40d3915a4 100644
--- a/content/public/test/browser_test_utils.h
+++ b/content/public/test/browser_test_utils.h
@@ -442,6 +442,10 @@ class DOMMessageQueue : public NotificationObserver,
   // message. Returns true on success.
   bool WaitForMessage(std::string* message) WARN_UNUSED_RESULT;
 
+  // If there is a message in the queue, then copies it to |message| and returns
+  // true.  Otherwise (if the queue is empty), returns false.
+  bool PopMessage(std::string* message) WARN_UNUSED_RESULT;
+
   // Overridden NotificationObserver methods.
   void Observe(int type,
                const NotificationSource& source,