cc: Add UMA stats for record and raster time.

cc/resources/tile_manager.cc

Index: cc/resources/tile_manager.cc
diff --git a/cc/resources/tile_manager.cc b/cc/resources/tile_manager.cc
index 5d183ae55290c5ef6909462f62c34fe3225d2b55..f66890dc67a9e86e859c1590dae3f4b40ff12632 100644
--- a/cc/resources/tile_manager.cc
+++ b/cc/resources/tile_manager.cc
@@ -12,6 +12,8 @@
 #include "base/json/json_writer.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/timer/elapsed_timer.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "cc/debug/devtools_instrumentation.h"
 #include "cc/debug/frame_viewer_instrumentation.h"
@@ -108,11 +110,18 @@ class RasterTaskImpl : public RasterTask {
   void Raster(const RasterSource* raster_source) {
     frame_viewer_instrumentation::ScopedRasterTask raster_task(
         tile_id_, tile_resolution_, source_frame_number_, layer_id_);
+    base::ElapsedTimer timer;
 
     DCHECK(raster_source);
 
     raster_buffer_->Playback(raster_source_.get(), content_rect_,
                              contents_scale_);
+
+    base::TimeDelta elapsed = timer.Elapsed();
+    UMA_HISTOGRAM_COUNTS("Renderer4.RasterTaskUs", elapsed.InMicroseconds());

[enne (OOO), 2015/04/08 20:18:46]

This one seems like a pretty good regression metric, although it is definitely
prone to influence by outside changes, e.g. image decoding improvements.

I think if we ever start rastering from the display list directly, it might be
worth having a "null canvas" microbenchmark, where we don't do any of the work,
but just iterate through it as if we were doing the work.

[jbroman, 2015/04/08 20:37:42]

Agreed. I think the best we're hoping for is to have a signal if we suddenly
make things dramatically worse in the real world.
Might be an interesting microbenchmark, sure, but it seems orthogonal to this
bug, no?

[enne (OOO), 2015/04/08 21:03:49]

Yeah.  Just trying to think out loud about more targeted metrics that might
better track the real performance issues with less noise.

+    UMA_HISTOGRAM_COUNTS(
+        "Renderer4.RasterTaskPixelsPerMs",
+        content_rect_.size().GetArea() / elapsed.InMillisecondsF());
   }
 
   RasterSource::SolidColorAnalysis analysis_;