Add RAIL tracing category to Chrome tracing.

media/blink/video_frame_compositor.cc

Index: media/blink/video_frame_compositor.cc
diff --git a/media/blink/video_frame_compositor.cc b/media/blink/video_frame_compositor.cc
index 3cf2a1cb22d85b54c9f9e6859097e5ac3693c4c7..400367e650ad6f24a5af72772b53088258981322 100644
--- a/media/blink/video_frame_compositor.cc
+++ b/media/blink/video_frame_compositor.cc
@@ -105,7 +105,7 @@ bool VideoFrameCompositor::HasCurrentFrame() {
 }
 
 void VideoFrameCompositor::Start(RenderCallback* callback) {
-  TRACE_EVENT0("media", "VideoFrameCompositor::Start");
+  TRACE_EVENT0("media,rail", "VideoFrameCompositor::Start");
 
   // Called from the media thread, so acquire the callback under lock before
   // returning in case a Stop() call comes in before the PostTask is processed.
@@ -118,7 +118,7 @@ void VideoFrameCompositor::Start(RenderCallback* callback) {
 }
 
 void VideoFrameCompositor::Stop() {
-  TRACE_EVENT0("media", "VideoFrameCompositor::Stop");
+  TRACE_EVENT0("media,rail", "VideoFrameCompositor::Stop");
 
   // Called from the media thread, so release the callback under lock before
   // returning to avoid a pending UpdateCurrentFrame() call occurring before