RenderFrameHostManagerTest* in content_browsertests is flaky.

Findit has detected 3 flake occurrences of tests below within
the past 24 hours:

RenderFrameHostManagerTest.CrossProcessPopupInheritsSandboxFlagsWithNoOpener
RenderFrameHostManagerTest.UpdateOpener

Please try to find and revert the culprit if the culprit is obvious.
Otherwise please find an appropriate owner.