Enable FlashFullscreenInteractiveBrowserTest.FullscreenFromSubframe

This test was disabled a while ago for issues with site isolation. At
this time the test passes 100 iterations locally, so I'll enable it for
now and hopefully the underlying flakiness is fixed.

Bug: 648406
Change-Id: I32ccea18e684a112753e90ea63c1daa80b8a2be8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1863591Reviewed-by: Yuri Wiitala <miu@chromium.org>
Commit-Queue: Nasko Oskov <nasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706118}

chrome/browser/ui/exclusive_access/flash_fullscreen_interactive_browsertest.cc

@@ -301,14 +301,8 @@ IN_PROC_BROWSER_TEST_F(FlashFullscreenInteractiveBrowserTest,
   EXPECT_TRUE(ObserveTabIsInFullscreen(false));
 }
 
-// Flaky on Linux, see https://crbug.com/648406.
-#if defined(OS_LINUX)
-#define MAYBE_FullscreenFromSubframe DISABLED_FullscreenFromSubframe
-#else
-#define MAYBE_FullscreenFromSubframe FullscreenFromSubframe
-#endif
 IN_PROC_BROWSER_TEST_F(FlashFullscreenInteractiveBrowserTest,
-                       MAYBE_FullscreenFromSubframe) {
+                       FullscreenFromSubframe) {
   ASSERT_TRUE(ui_test_utils::BringBrowserWindowToFront(browser()));
   StartFakingTabCapture();
   ASSERT_TRUE(LaunchFlashFullscreenInSubframe());