Prepare MimeHanderViewContainer for removing swapped out RenderFrame.

The current implementation of MimeHanderViewContainer is dependent on
the usage of swapped out RenderFrame for the out-of-process component.
Since swapped out state is going away, this CL removes this dependency.

Credit goes to dcheng@, who found the simplest solution.

BUG=357747

Review URL: https://codereview.chromium.org/1335023004

Cr-Commit-Position: refs/heads/master@{#348666}
1 file changed