Drop dependency on webrtc's tick_utils.h.

content/renderer/media/webrtc/media_stream_remote_video_source.cc

Index: content/renderer/media/webrtc/media_stream_remote_video_source.cc
diff --git a/content/renderer/media/webrtc/media_stream_remote_video_source.cc b/content/renderer/media/webrtc/media_stream_remote_video_source.cc
index 8bac9d7047e3817855d318da26bb11e93701d2f2..b82695e2137cdb10d4f6839b6931d1ac4b1c1cd2 100644
--- a/content/renderer/media/webrtc/media_stream_remote_video_source.cc
+++ b/content/renderer/media/webrtc/media_stream_remote_video_source.cc
@@ -19,7 +19,6 @@
 #include "media/base/video_util.h"
 #include "third_party/webrtc/media/base/videoframe.h"
 #include "third_party/webrtc/media/base/videosinkinterface.h"
-#include "third_party/webrtc/system_wrappers/include/tick_util.h"
 
 namespace content {
 
@@ -71,8 +70,7 @@ MediaStreamRemoteVideoSource::RemoteVideoSourceDelegate::
       // the offset, 2) the rate (i.e., one clock runs faster than the other).
       // See http://crbug/516700
       time_diff_(base::TimeTicks::Now() - base::TimeTicks() -

[perkj_webrtc, 2016/04/14 13:46:23]

Isn't all these methods from the same clock in the same base?  ie- Isn't this
always 0? 

[nisse-webrtc, 2016/04/19 11:12:41]

I haven't yet tried to understand time sources in chrome. Hopefully they're all
clock_gettime(CLOCK_MONOTONIC), or some analogous clock on non-posix systems.

time_diff_ was added in cl https://codereview.chromium.org/1320183003, it seems.

-                 base::TimeDelta::FromMicroseconds(
-                     webrtc::TickTime::MicrosecondTimestamp())) {}
+                 base::TimeDelta::FromMicroseconds(rtc::TimeMicros())) {}
 
 MediaStreamRemoteVideoSource::
 RemoteVideoSourceDelegate::~RemoteVideoSourceDelegate() {