Add performance tracing event to VideoCaptureDeviceAndroid::OnFrameAvailable

media/video/capture/android/video_capture_device_android.cc

Index: media/video/capture/android/video_capture_device_android.cc
diff --git a/media/video/capture/android/video_capture_device_android.cc b/media/video/capture/android/video_capture_device_android.cc
index adfa9a3455c12bf5293b8fd1aae87a5a965a472c..7eeffbe0b11bf8c9b8cf157bc4004f1a552148d4 100644
--- a/media/video/capture/android/video_capture_device_android.cc
+++ b/media/video/capture/android/video_capture_device_android.cc
@@ -9,6 +9,7 @@
 #include "base/android/jni_android.h"
 #include "base/android/jni_string.h"
 #include "base/android/scoped_java_ref.h"
+#include "base/debug/trace_event.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "jni/VideoCapture_jni.h"
@@ -196,6 +197,7 @@ void VideoCaptureDeviceAndroid::OnFrameAvailable(
     jbyteArray data,
     jint length,
     jint rotation) {
+  TRACE_EVENT0("video", "VideoCaptureDeviceAndroid::OnFrameAvailable");

[tommi (sloooow) - chröme, 2013/12/18 14:01:33]

Since Android is very sensitive to performance I have to ask... is there a
performance impact of doing this?
Will we change the outcome by measuring it?

[mcasas, 2013/12/18 14:32:36]

Well, nothing comes for free. From the docs:

"
Trace macros are very low overhead. When tracing is 
not turned on, trace macros cost at most a few dozen
clocks. When running, trace macros cost a few thousand 
clocks at most. Arguments to the trace macro are 
evaluated only when tracing is on --- if tracing is 
off, the value of the arguments dont get computed.
"

Consider wrapping around a #if !defined(NDEBUG) ?

[tommi (sloooow) - chröme, 2013/12/18 15:14:33]

That's good enough for me.  I know how this is implemented on other platforms
but don't know how it's done on Android.  Given the documentation this sounds
like an expected use case.

   DVLOG(3) << "VideoCaptureDeviceAndroid::OnFrameAvailable: length =" << length;
 
   base::AutoLock lock(lock_);