[wip/exp] cc: Measure the amount of overdraw.

ash/system/tray/system_tray_unittest.cc

Index: ash/system/tray/system_tray_unittest.cc
diff --git a/ash/system/tray/system_tray_unittest.cc b/ash/system/tray/system_tray_unittest.cc
index c8dc570c4f0103ed481221f980abfc7c284330cf..92c794c25577405aa05bfb382c1e265d8281fc48 100644
--- a/ash/system/tray/system_tray_unittest.cc
+++ b/ash/system/tray/system_tray_unittest.cc
@@ -27,6 +27,7 @@
 #include "base/test/histogram_tester.h"
 #include "ui/base/ui_base_types.h"
 #include "ui/compositor/scoped_animation_duration_scale_mode.h"
+#include "ui/compositor/test/draw_waiter_for_test.h"
 #include "ui/events/test/event_generator.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/rect.h"
@@ -306,6 +307,8 @@ TEST_F(SystemTrayTest, SystemTrayColoringAfterAlignmentChange) {
   RunAllPendingInMessageLoop();
   // The bubble should already be closed by now.
   ASSERT_FALSE(tray->CloseSystemBubble());
+
+  ui::DrawWaiterForTest::WaitForCommit(tray->GetWidget()->GetCompositor());
 }
 
 TEST_F(SystemTrayTest, SystemTrayTestItems) {