Added cleanup to decoding of monochrome frames.
Added cleanup to decoding of monochrome frames.

If the frame's monochrome flag is set, the decoded frame
will be given constant chroma planes, regardless of any
chroma data in the original frame.

Change-Id: I9ea078f02c279ae9ec1d23cc33f69c6abcb18b9f

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom