Handle Ctrl-C on the main thread during android setup properly.

If we got an interrupt on the main thread, we wouldn't shut down
the pool of threads initializing devices properly and the threads
would continue to execute in the background.

R=peter@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/24191006

git-svn-id: svn://svn.chromium.org/blink/trunk@158112 bbb929c8-8fbe-4397-9dbb-9b2b20218538