Disabling RenderFrameHostImplBrowserTest.IsFocused_AtLoad due to flaky failures

http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=RenderFrameHostImplBrowserTest.IsFocused_Change&testType=content_browsertests

BUG=452631
TBR=mlamouri@chromium.org

Review URL: https://codereview.chromium.org/865063003

Cr-Commit-Position: refs/heads/master@{#313356}

content/browser/frame_host/render_frame_host_impl_browsertest.cc

@@ -65,7 +65,9 @@ IN_PROC_BROWSER_TEST_F(RenderFrameHostImplBrowserTest, IsFocused_AtLoad) {
 }
 
 // Test that if the content changes the focused frame, it is correctly exposed.
-IN_PROC_BROWSER_TEST_F(RenderFrameHostImplBrowserTest, IsFocused_Change) {
+// Disabled to to flaky failures: crbug.com/452631
+IN_PROC_BROWSER_TEST_F(RenderFrameHostImplBrowserTest,
+                       DISABLED_IsFocused_Change) {
   EXPECT_TRUE(
       NavigateToURL(shell(), GetTestUrl("render_frame_host", "focus.html")));