Roll libvpx 166959:861f35

Build VP9 postproc/mfqe for WebRTC
https://codereview.chromium.org/1033873004

R=marpan@google.com, tomfinegan@chromium.org

Review URL: https://codereview.chromium.org/1009963004

Cr-Commit-Position: refs/heads/master@{#322488}

DEPS

@@ -40,7 +40,7 @@ vars = {
   'pdfium_git': 'https://pdfium.googlesource.com',
   'skia_git': 'https://skia.googlesource.com',
   'boringssl_git': 'https://boringssl.googlesource.com',
-  'libvpx_revision': '166959c4d8f3c84ed730ca8e7ff1ba5c921bc665',
+  'libvpx_revision': '861f35b01c87a021540aace739cb7415c08e987b',
   'sfntly_revision': '1bdaae8fc788a5ac8936d68bf24f37d977a13dac',
   'skia_revision': 'e0b19d4985846d64bb581013828a9dc5af401a5d',
   # Three lines of non-changing comments so that