telemetry: Add enable-gpu-benchmarking extension back to smoothness
The enable-gpu-benchmarking flag has been removed from smoothness measurement
in https://codereview.chromium.org/
183683020/. Under the assumption that
metrics that need it will automatically set the flag. This is only true
for synthetic gestures, but not for the wait action. Therefore
smoothness.tought_canvas_cases and smoothness.tought_animation_cases failed
after the patch landed. This CL add the enable-gpu-benchmarking flag back
to the smoothness measurement.
TBR=tonyg@chromium.org,isherman@chromium.org
BUG=349338
NOTRY=True
Review URL: https://codereview.chromium.org/
183973032
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255084 0039d316-1c4b-4281-b951-d872f2087c98