Add one more logging.exception to gpu integration test.

BUG=1005971
TEST=bots
TBR=kbr@chromium.org

Change-Id: I7fa855164374230c6846336c1d3d33f0160546e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1817287Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Commit-Queue: Zhenyao Mo <zmo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#698726}

content/test/gpu/gpu_tests/gpu_integration_test.py

@@ -175,6 +175,7 @@ class GpuIntegrationTest(
     except Exception:
       if ResultType.Failure in expected_results or should_retry_on_failure:
         if should_retry_on_failure:
+          logging.exception('Exception while running flaky test %s', test_name)
           # For robustness, shut down the browser and restart it
           # between flaky test failures, to make sure any state
           # doesn't propagate to the next iteration.