Upgrade libvpx to 6b66c01 and enabling temporal denoising.
Upgrade libvpx to 6b66c01 and enabling temporal denoising.

BUG=
TEST=

Review URL: http://webrtc-codereview.appspot.com/448006

git-svn-id: 9b397c5dfe384c04b1b200d5305b653241000171@1908 4adac7df-926f-26a2-2b94-8c16560cd09d

lukeweber/webrtc-src-override,lukeweber/webrtc-src-override,lukeweber/webrtc-src-override,lukeweber/webrtc-src-override,lukeweber/webrtc-src-override,lukeweber/webrtc-src-override,lukeweber/webrtc-src-override