add an exhaustic yuv color space test, and relax yuv conversion results to allow for future change. BUG=324 TESTED=TestFullYUV R=harryjin@google.com
add an exhaustic yuv color space test, and relax yuv conversion results to allow for future change.
BUG=324
TESTED=TestFullYUV
R=harryjin@google.com

Review URL: https://webrtc-codereview.appspot.com/37689004
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