Revert 86681 - Updated OMX decoder for recent PPAPI changes, and added to the build.

Revert 86681 - Updated OMX decoder for recent PPAPI changes, and added to the build.

Had to move from content/gpu to content/common/gpu to allow gpu_video_service.cc
to depend on the decoder.
Removed some dead code and did some random cleanup while I was in there.

BUG=none
TEST=chrome compiles on cros/arm!

Review URL: http://codereview.chromium.org/7057027

TBR=fischman@chromium.org
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=86687