Fix flakiness in DragAndDropBrowserTests

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 ac767bb53e1aa2a96b8d25b7332ce12c951673ec..39388b1995e4fcf9aae47e47f3dc325689403302 100644
--- a/content/public/test/browser_test_utils.h
+++ b/content/public/test/browser_test_utils.h
@@ -351,6 +351,12 @@ void WaitForGuestSurfaceReady(content::WebContents* web_contents);
 
 #endif
 
+// Waits until the cc::Surface associated with a cross-process child frame
+// has been drawn for the first time. Once this method returns it should be
+// safe to assume that events sent to the top-level RenderWidgetHostView can
+// be expected to properly hit-test to this surface, if appropriate.
+void WaitForChildFrameSurfaceReady(content::RenderFrameHost* child_frame);
+
 // Watches title changes on a WebContents, blocking until an expected title is
 // set.
 class TitleWatcher : public WebContentsObserver {