cros: Clean up EventRouter observer for TtsExtensionLoaderChromeOs

It was registering one but not cleaning it up.

BUG=323345
TEST=see bug
R=dmazzoni@chromium.org

Review URL: https://codereview.chromium.org/88793002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237378 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237378
Add assets for android context menu tests

BUG=277135
NOTRY=true

Review URL: https://codereview.chromium.org/85653006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237379 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237379