Mark 4 DumpAccessibilityTreeTest tests flaky

The following tests are flaky on all platforms:
- DumpAccessibilityTreeTest.AccessibilityIframeTransform
- DumpAccessibilityTreeTest.AccessibilityIframeCoordinates
- DumpAccessibilityTreeTest.AccessibilityIframeCoordinatesCrossProcess
- DumpAccessibilityTreeTest.AccessibilityIframeTransformCrossProcess

http://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=content_browsertests&tests=DumpAccessibilityTreeTest.AccessibilityIframe

NOTREECHECKS=true
NOTRY=true
BUG=622387
TBR=dmazzoni@chromium.org

Review-Url: https://codereview.chromium.org/2282903002
Cr-Commit-Position: refs/heads/master@{#414737}
1 file changed