Disable flaky AccessibilityFullscreenBrowserTest.InsideIFrame

The test fails flakily on Linux, Windows and ChromeOS.
See bug for details.

TBR=foolip@chromium.org, dmazzoni@chromium.org

Bug: 825735
Change-Id: I5953f23c9c87e7b4ab2b0a6b9fd9d604a1bf27c3
Reviewed-on: https://chromium-review.googlesource.com/979799Reviewed-by: Dominic Battré <battre@chromium.org>
Commit-Queue: Dominic Battré <battre@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545739}

content/browser/accessibility/fullscreen_browsertest.cc

@@ -106,7 +106,9 @@ IN_PROC_BROWSER_TEST_F(AccessibilityFullscreenBrowserTest,
   EXPECT_EQ(1, CountLinks(manager->GetRoot()));
 }
 
-IN_PROC_BROWSER_TEST_F(AccessibilityFullscreenBrowserTest, InsideIFrame) {
+// Fails flakily on all platforms: crbug.com/825735
+IN_PROC_BROWSER_TEST_F(AccessibilityFullscreenBrowserTest,
+                       DISABLED_InsideIFrame) {
   ASSERT_TRUE(embedded_test_server()->Start());
 
   FakeFullscreenDelegate delegate;