ui_tests: check the return value of WaitForAppLaunch.
ui_tests: check the return value of WaitForAppLaunch.

This function has a return value.  We should abort the test if it
fails.

BUG=45115
TEST=EarlyReturnTest.ToastCrasher, which times out, should go red
(I preemptively disabled it)

Review URL: http://codereview.chromium.org/3470014

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@60506 0039d316-1c4b-4281-b951-d872f2087c98

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