Use TRACE_EVENT to track time spent in VP8 encoding

Using the TRACE_EVENT macro to log VP8 encoding events.
Review URL: https://webrtc-codereview.appspot.com/968011

git-svn-id: http://webrtc.googlecode.com/svn/trunk@3264 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc

@@ -27,6 +27,7 @@
 #include "modules/video_coding/codecs/vp8/reference_picture_selection.h"
 #include "modules/video_coding/codecs/vp8/temporal_layers.h"
 #include "system_wrappers/interface/tick_util.h"
+#include "system_wrappers/interface/trace_event.h"
 
 enum { kVp8ErrorPropagationTh = 30 };
 
@@ -384,6 +385,9 @@ int VP8EncoderImpl::Encode(const I420VideoFrame& input_image,
                               input_image.timestamp());
   }
 
+  TRACE_EVENT1("video_coding", "VP8EncoderImpl::Encode",
+               "input_image_timestamp", input_image.timestamp());
+
   // TODO(holmer): Ideally the duration should be the timestamp diff of this
   // frame and the next frame to be encoded, which we don't have. Instead we
   // would like to use the duration of the previous frame. Unfortunately the