Adjust pixel count threshold for ui tests.

In a ui_SystemTray test, the test will fail if the diff pixel count is >
0. We need to be a bit more linient in this area.

Based on previous test results, we see that a diff count of 34 is still
a good image and shouldn't fail the test.

BUG=chromium:374981
TEST=Ran local test on link.

Change-Id: I579adbd711f3330fa4b186b3f035e6ec74bf12f7
Reviewed-on: https://chromium-review.googlesource.com/220553
Reviewed-by: Rohit Makasana <rohitbm@chromium.org>
Commit-Queue: Mussa Kiroga <mussa@chromium.org>
Tested-by: Mussa Kiroga <mussa@chromium.org>
2 files changed