Possible fix for flaky browser test.

Bug: 1124982, b/168119903
Change-Id: Ifd971c6ad521f436e2af79d168bc643704575690
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2401046
Commit-Queue: John Williams <jrw@chromium.org>
Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806009}

chrome/browser/ui/views/media_router/media_router_ui_browsertest.cc

@@ -39,8 +39,8 @@
 
 namespace media_router {
 
-// Base class containing setup code and test cases shared between WebUI and
-// Views dialog tests.
+// Base class containing setup code and test cases shared between Views dialog
+// tests.
 class MediaRouterUIBrowserTest : public InProcessBrowserTest {
  public:
   MediaRouterUIBrowserTest()
@@ -78,6 +78,7 @@ class MediaRouterUIBrowserTest : public InProcessBrowserTest {
     GetCastIcon()->OnMousePressed(
         ui::MouseEvent(ui::ET_MOUSE_PRESSED, gfx::Point(0, 0), gfx::Point(0, 0),
                        ui::EventTimeForNow(), ui::EF_LEFT_MOUSE_BUTTON, 0));
+    base::RunLoop().RunUntilIdle();
   }
 
   bool ToolbarIconExists() {