[Extensions] Remove manifest v1 support for accessible resources

In manifest version 1, all extension resources were considered
accessible by the web (i.e., could be embedded within or
requested by a web page). In manifest v2, only resources
explicitly specified in the web_accessible_resources key are
accessible. Remove support for manifest v1, and always check
the web accessible resources.

Update unit tests to migrate relevant tests and remove tests for
manifest v1-specific behavior.

Bug: 816677, 816679
Change-Id: Id0dd3ef75cd5d49e3f87e45ac3a8b19a00391146
Reviewed-on: https://chromium-review.googlesource.com/953177
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545898}
12 files changed