Flakiness dashboard shows this test has become very flaky around r418790 on 9/14/2016:

https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=interactive_ui_tests&tests=FlashFullscreenInteractiveBrowserTest.FullscreenFromSubframe

It appears to only be flaky with --site-per-process on Linux (affecting both linux_site_isolation try bot and Site Isolation Linux FYI bot).  Site Isolation Win is unaffected.

Sample failure: https://build.chromium.org/p/tryserver.chromium.linux/builders/linux_site_isolation/builds/3421

Output:
[ RUN      ] FlashFullscreenInteractiveBrowserTest.FullscreenFromSubframe
Xlib:  extension "RANDR" missing on display ":9".
Xlib:  extension "RANDR" missing on display ":9".
[24915:24915:0919/004538:WARNING:audio_manager.cc(317)] Multiple instances of AudioManager detected
[24915:24915:0919/004538:WARNING:audio_manager.cc(278)] Multiple instances of AudioManager detected
[24915:24915:0919/004538:WARNING:password_store_factory.cc(248)] Using basic (unencrypted) store for password storage. See https://chromium.googlesource.com/chromium/src/+/master/docs/linux_password_storage.md for more information about password storage options.
[24915:24971:0919/004539:WARNING:simple_synchronous_entry.cc(1054)] Could not open platform files for entry.
[24915:24915:0919/004539:WARNING:render_frame_host_impl.cc(2060)] OnDidStopLoading was called twice.
[24915:24915:0919/004539:INFO:CONSOLE(178)] "EnterFullscreen finished in 0.013 seconds.", source: http://127.0.0.1:52353/test_case.html?testcase=FlashFullscreenForBrowserUI (178)
../../chrome/test/ppapi/ppapi_test.cc:249: Failure
Value of: handler.message().c_str()
  Actual: "EnterFullscreen FAIL: IsFullscreen() in fullscreen failed with error: 0"
Expected: "PASS"
../../chrome/browser/ui/exclusive_access/flash_fullscreen_interactive_browsertest.cc:114: Failure
Failed
Failed to launch simulated fullscreen Flash plugin.  Interactive UI testing cannot proceed.
../../chrome/browser/ui/exclusive_access/flash_fullscreen_interactive_browsertest.cc:311: Failure
Value of: LaunchFlashFullscreenInSubframe()
  Actual: false
Expected: true
[24915:24915:0919/004539:WARNING:url_request_context_getter.cc(43)] URLRequestContextGetter leaking due to no owning thread.
[  FAILED  ] FlashFullscreenInteractiveBrowserTest.FullscreenFromSubframe, where TypeParam =  and GetParam() =  (622 ms)

I'll disable the test until we have a chance to investigate this.