Convert ExtensionRegistry to a BrowserContextKeyedService

This removes dependencies on ExtensionService, which does not exist for
app_shell.

* Convert all of src/extensions to use ExtensionRegistry's extension sets.
* Remove ExtensionService::blacklisted_extensions() and convert all callers
  to use ExtensionRegistry.

BUG=none
TEST=existing unit_tests, browser_tests
R=miket@chromium.org
TBR=phajden.jr@chromium.org for adding dependency on components/browser_context_keyed_service

Review URL: https://codereview.chromium.org/120863003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242624 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242624