TextTrackLoaderClient should not be a ResourceOwner.

TextTrackLoaderClient is a ResourceOwner<RawResource>, but it doesn't hold
a Resource. Hence it doesn't need to inherit the class.

BUG=None

Review URL: https://codereview.chromium.org/1471283006

Cr-Commit-Position: refs/heads/master@{#363153}
2 files changed