NOT READY FOR REVIEW - switch to a subscriber model for rendering stats

cc/layer_tree_host_impl.cc

Index: cc/layer_tree_host_impl.cc
diff --git a/cc/layer_tree_host_impl.cc b/cc/layer_tree_host_impl.cc
index 581377e2b3397ef5f3c4eea7e8502b62b7626621..41d66499587e9d2ff8cb84b0dd96307abc061614 100644
--- a/cc/layer_tree_host_impl.cc
+++ b/cc/layer_tree_host_impl.cc
@@ -25,6 +25,7 @@
 #include "cc/prioritized_texture_manager.h"
 #include "cc/render_pass_draw_quad.h"
 #include "cc/rendering_stats.h"
+#include "cc/rendering_stats_subscriber.h"
 #include "cc/scrollbar_animation_controller.h"
 #include "cc/scrollbar_layer_impl.h"
 #include "cc/settings.h"
@@ -676,7 +677,10 @@ void LayerTreeHostImpl::drawLayers(const FrameData& frame)
     // FIXME: use the frame begin time from the overall compositor scheduler.
     // This value is currently inaccessible because it is up in Chromium's
     // RenderWidget.
-    m_fpsCounter->markBeginningOfFrame(base::TimeTicks::Now());
+    base::TimeTicks now = base::TimeTicks::Now();
+    m_fpsCounter->markBeginningOfFrame(now);
+    if (m_renderingStatsSubscriber)
+        m_renderingStatsSubscriber->markBeginningOfFrame(now);
 
     if (m_settings.showDebugRects())
         m_debugRectHistory->saveDebugRectsForCurrentFrame(m_rootLayerImpl.get(), *frame.renderSurfaceLayerList, frame.occludingScreenSpaceRects, settings());
@@ -1472,6 +1476,26 @@ void LayerTreeHostImpl::renderingStats(RenderingStats* stats) const
     stats->numMainThreadScrolls = m_numMainThreadScrolls;
 }
 
+void LayerTreeHostImpl::startRecordingRenderingStats()
+{
+    m_renderingStatsSubscriber = RenderingStatsSubscriber::create();
+}
+
+void LayerTreeHostImpl::stopRecordingRenderingStats(RenderingStats* stats)
+{
+    double frame_rate_average = 0.0;
+    double frame_rate_standard_deviation = 0.0;
+
+    m_renderingStatsSubscriber->getFPSAndStandardDeviation(
+        frame_rate_average,
+        frame_rate_standard_deviation);
+
+    stats->frameRateAverage = frame_rate_average;
+    stats->frameRateStandardDeviation = frame_rate_standard_deviation;
+
+    m_renderingStatsSubscriber.reset();
+}
+
 void LayerTreeHostImpl::animateScrollbars(base::TimeTicks time)
 {
     animateScrollbarsRecursive(m_rootLayerImpl.get(), time);