GitLab

According to crbug.com/128644
- the mute icon should be in the tray if volume is 0%
- volume slider point has to be 0.0 when muted

BUG=128644
TEST=manually

Review URL: https://chromiumcodereview.appspot.com/10408036

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@138282 0039d316-1c4b-4281-b951-d872f2087c98