Refactor some ProfileSyncServiceTests

Create a new test framework class named ProfileSyncServiceSimpleTest and
use it to replace several ProfileSyncServiceTests.  This newer framework
takes advantage of MockSyncBackendHost and allows us to use a real
ProfileSyncService in these tests.

The resulting tests are better at testing the ProfileSyncService, but
they no longer test any part of the SyncBackendHost code.   This is a
desirable trade off because these are unit tests.

BUG=312994

Review URL: https://codereview.chromium.org/69583002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235661 0039d316-1c4b-4281-b951-d872f2087c98
chromeos: Brightness policies for PowerPolicyController.

Add support to PowerPolicyController for controlling the
screen brightness. This isn't controlled by any prefs or
enterprise policies yet.

BUG=310429

Review URL: https://codereview.chromium.org/69813007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235662 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235662
Fix browser crash when calling MediaPlayerBridge::PrepareAsync

BUG=319956

Review URL: https://codereview.chromium.org/74293002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235663 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235663