Make Content Shell's bundle layout mirror Chromium.

This moves the Content Shell Helper from:

  Content Shell.app/Contents/Frameworks/Content Shell Helper.app

To:

  Content Shell.app/Contents/Frameworks/Content Shell Framework.framework/Helpers/Content Shell Helper.app

This will make it easier to support multiple variants of the Helper app
that will be granted different code signing entitlements. While
Content Shell does not get signed, the process launching code lives in
//content, and so Content Shell needs to have a similar layout to Chrome
for launching the helper variants.

Bug: 958976
Change-Id: I5d9cebe38160c9306f0346b94d5d8346577bf5ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1612131
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660127}
4 files changed