Auto merge of #1198 - JerryShih:resolve-ext-image, r=glennw
Auto merge of #1198 - JerryShih:resolve-ext-image, r=glennw

Resolve the ext-image again even though it's resolved in previous frame.

r? @kvark @glennw

Maybe we will do the partial updating for the frame data(scrolling?). So, the SourceTexture in cpu_yuv_image is not in a invalid status. Then, we will skip that ext-image resolving. Thus, it will not be put into the deferred_resolves list. Finally, we can't resolve that ext-image in renderer.
In this patch, we will always resolve the yuv images for every frame.

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