Don't show the Translate bubble when the tab is not focused

BUG=317431
TEST=manual
TBR=sky@chromium.org

Review URL: https://codereview.chromium.org/80493002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237051 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237051