Fail pixel tests when reference images are missing from cloud storage.

Fail pixel tests when reference images are missing from cloud storage.

Turn the exception into a test failure which can be suppressed via the
test expectations.

Verified locally with a run that triggered the exception.
Confirmed the failures can be suppressed.

BUG=349262
TEST=./content/test/gpu/run_gpu_test.py pixel --browser=release --build-revision 270401 --download-refimg-from-cloud-storage --refimg-cloud-storage-bucket chromium-gpu-archive/reference-images --os-type linux --test-machine-name [fake name]
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=270498

[Ken Russell (switch to Gerrit), 2014-05-14 17:48:45]

Brandon, Mo: please review.

Dana: FYI.

[bajones, 2014-05-14 18:36:20]

lgtm

[Ken Russell (switch to Gerrit), 2014-05-14 18:36:43]

The CQ bit was checked by kbr@chromium.org

[commit-bot: I haz the power, 2014-05-14 18:37:28]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/kbr@chromium.org/281193002/1

[commit-bot: I haz the power, 2014-05-14 22:26:40]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  ios_dbg_simulator on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_dbg_simulator/bui...)
  linux_chromium_chromeos_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_chrome...)
  linux_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_rel/bu...)

[commit-bot: I haz the power, 2014-05-14 22:31:33]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-05-14 22:31:33]

Try jobs failed on following builders:
  ios_dbg_simulator on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/ios_dbg_simulator/bui...)

[Ken Russell (switch to Gerrit), 2014-05-14 22:53:10]

These try job failures are unrelated to this CL. I'm marking it NOTRY=true in
order to unblock other work.

[Ken Russell (switch to Gerrit), 2014-05-14 22:53:22]

The CQ bit was checked by kbr@chromium.org

[commit-bot: I haz the power, 2014-05-14 22:54:11]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/kbr@chromium.org/281193002/1

[commit-bot: I haz the power, 2014-05-14 23:04:32]

Change committed as 270498