Raise an exception when a non glob test expectation pattern is shorter than any test name

If a test expectations non glob pattern is shorter than any test name then the presubmit
check should raise an exception because the test expectation is for a non existing test.
This CL will update CheckTestExpectationsAreForExistingTests so that it raises an exception
when it finds one of these test expectations.

Bug: chromium:978712
Change-Id: Ic80efccca659b7f35a345ebb187fb7dab08c423f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1677510
Commit-Queue: Rakib Hasan <rmhasan@google.com>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672693}

• content/test/gpu/gpu_tests/test_expectations_unittest.py[diff]