Fix media media_blink_unittest
Fix media media_blink_unittest

VideoFrameCompositorTest.NaturalSizeChanged & VideoFrameCompositorTest.OpacityChanged broke
while the tests were not running. Most likely because of https://codereview.chromium.org/1299523002/
This fixes the test.

Review URL: https://codereview.chromium.org/1339373003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#348938}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk