Add gpu pixel test expectations for webview

Add expectations for android-webview-instruemtation. Tests that are not
expected to ever pass are marked skip. Tests that will pass once there
are reference images are marked fail.

Note there are some conflicts with existing expectations on android.
Generally prefer to keep existing expectatioon.

Bug: 941467
Change-Id: Iae6ad90104160ec2775e1a5a15ccf3466c064e2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1531526
Commit-Queue: Bo <boliu@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#645605}