Bug 1020538 - Re-enable test_playback_rate.html on Linux, OSX, and Android. r=cpearce
No bug - Clean up media mochitest manifests.

This doesn't change the enabled/disabled state of any tests. It should be a no-op since the harness runs tests alphabetically anyway regardless of their order in the manifest.
Bug 1008310 - WebGL warning for using element array with different types. r=jgilbert
Bug 1019244 - Do not throw on exception handling during xpcshell tests. r=ted
Bug 1020581 - Notification resend test feedback improvement and less strict on timestamp. r=mhenretty