Added missing import.

I accidentally blew away my changes just before the last commit and
made a mistake while recreating it.

BUG=365904,368107
TBR=bajones@chromium.org

Review URL: https://codereview.chromium.org/259363002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@266930 0039d316-1c4b-4281-b951-d872f2087c98

content/test/gpu/gpu_tests/context_lost.py

@@ -4,6 +4,7 @@
 import os
 
 from telemetry import test as test_module
+from telemetry.core import exceptions
 from telemetry.core import util
 from telemetry.page import page_set
 from telemetry.page import page_test