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The previous theories haven't held up, so these crash keys will help
reveal how the proxy is being created.  They cover all the ways of
reaching the RenderFrameProxy constructor (i.e., RVI::Initialize,
RFI::OnSwapOut, and RTI::OnCreateNewFrameProxy).

BUG=575245
TEST=New crash keys present in crash reports.

Review URL: https://codereview.chromium.org/1643673002

Cr-Commit-Position: refs/heads/master@{#371857}