Clean up test results for Web Animations virtual suite

The web-animations-css virtual suite runs the animations LayoutTests with Web
Animations enabled. This is a work in progress so many tests currently fail.

This change cleans up the existing expected results and expectations for
failing tests ...
- Modify a helper to not log flaky debug information in case of failure
- Remove platform-specific expected results
- Use failing platform-generic expected results where possible
- Use failing expectations for tests which can't be rebaselined

BUG=274667,258896
R=dstockwell

Review URL: https://chromiumcodereview.appspot.com/22999024

git-svn-id: svn://svn.chromium.org/blink/trunk@156283 bbb929c8-8fbe-4397-9dbb-9b2b20218538