Sets render_frame_proxy_ to null in the RenderFrameImpl when destroying the RenderFrameProxy.

This fixes with a use-after-free in the RenderFrameProxy reported by the asan bots, but uncovers another one.

TEST=NavigateRemoteFrame
BUG=357747

Review URL: https://codereview.chromium.org/929463004

Cr-Commit-Position: refs/heads/master@{#316337}
1 file changed