GPU: Add trace for real SwapBuffers.

ui/gl/gl_surface_egl.cc

Index: ui/gl/gl_surface_egl.cc
diff --git a/ui/gl/gl_surface_egl.cc b/ui/gl/gl_surface_egl.cc
index d11577b3fd10f621f3d028b3d75198ec4793e4d0..b6a7184c129f7e3e18588c69864f775420ab7ae3 100644
--- a/ui/gl/gl_surface_egl.cc
+++ b/ui/gl/gl_surface_egl.cc
@@ -13,6 +13,7 @@
 #endif
 
 #include "base/command_line.h"
+#include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop.h"
@@ -394,6 +395,10 @@ bool NativeViewGLSurfaceEGL::IsOffscreen() {
 }
 
 bool NativeViewGLSurfaceEGL::SwapBuffers() {
+  TRACE_EVENT2("gpu", "NativeViewGLSurfaceEGL:RealSwapBuffers",
+      "width", GetSize().width(),
+      "height", GetSize().height());
+
   if (!eglSwapBuffers(GetDisplay(), surface_)) {
     DVLOG(1) << "eglSwapBuffers failed with error "
              << GetLastEGLErrorString();