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When a package is selected in the file opener, it is automatically zipped, and
the zipped file is passed to the render view host.

This CL fixes 2 unrelated bugs in file_select_helper:
- If the render_view_host_ was destroyed before the user finished with the
file_select_helper, then Release() would never be called and the
file_select_helper would leak.

- If the render_view_host_ was destroyed before the user finished with the
file_select_helper, the default directory would be updated if the user was
opening multiple files, but it would not be updated if the user was opening a
single file. Now both update the default directory.

Note: When a large package is being zipped, the UI thread and renderer are
still responsive, but display no indication of the ongoing work.

BUG=33920

Review URL: https://codereview.chromium.org/634833003

Cr-Commit-Position: refs/heads/master@{#299143}