Roll WebRTC 8646:8649

WebRTC 8646:8649
Changes: https://chromium.googlesource.com/external/webrtc/trunk/webrtc.git/+log/a2bd4b8..b4c07a0

TBR=

Review URL: https://codereview.chromium.org/994503002

Cr-Commit-Position: refs/heads/master@{#319610}

DEPS

@@ -230,7 +230,7 @@ deps = {
    Var('chromium_git') + '/native_client/src/third_party/scons-2.0.1.git' + '@' + '1c1550e17fc26355d08627fbdec13d8291227067',
 
   'src/third_party/webrtc':
-    Var('chromium_git') + '/external/webrtc/trunk/webrtc.git' + '@' + 'a2bd4b8fc612dbbee9d108b96587d0c04f0b0df3',
+    Var('chromium_git') + '/external/webrtc/trunk/webrtc.git' + '@' + 'b4c07a05db526b5166a2ceb4df26f987d1209ff1',
 
   'src/third_party/openmax_dl':
     Var('chromium_git') + '/external/webrtc/deps/third_party/openmax.git' + '@' +  Var('openmax_dl_revision'),