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This CL makes the following improvements to extraction of the chrome
archive and installer from the mini_installer:

- Better documentation on OnResourceFound
- Resources are only written to disk once all other operations have
  succeeded.
- The output file is deleted in case of mid-write error (e.g., disk
  full).
- Duplicate resources lead to failure (e.g., two resources named
  "chrome*").
- Error codes from write failures now bubble up to ExtraCode1.

BUG=516207

Change-Id: I9a3b69ee59421116a175914b1f2d16f9eb15b688
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2302629
Commit-Queue: Greg Thompson <grt@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789761}