cc: Turn overdraw metrics on only when about:tracing is recording.

cc/quad_culler_unittest.cc

Index: cc/quad_culler_unittest.cc
diff --git a/cc/quad_culler_unittest.cc b/cc/quad_culler_unittest.cc
index c60aec60b5bbad98896c48a53af5dfd34a89147f..433d489f8ae02f09488a8384c69efa50c0b9c222 100644
--- a/cc/quad_culler_unittest.cc
+++ b/cc/quad_culler_unittest.cc
@@ -224,7 +224,7 @@ TEST(QuadCullerTest, verifyCullCenterTileNonIntegralSize1)
     appendQuads(quadList, sharedStateList, rootLayer.get(), it, occlusionTracker);
     EXPECT_EQ(quadList.size(), 2u);
 
-    EXPECT_NEAR(occlusionTracker.overdrawMetrics().pixelsDrawnOpaque(), 20363, 1);
+    EXPECT_NEAR(occlusionTracker.overdrawMetrics().pixelsDrawnOpaque(), 20000, 1);
     EXPECT_NEAR(occlusionTracker.overdrawMetrics().pixelsDrawnTranslucent(), 0, 1);
     EXPECT_NEAR(occlusionTracker.overdrawMetrics().pixelsCulledForDrawing(), 0, 1);
 }
@@ -252,7 +252,7 @@ TEST(QuadCullerTest, verifyCullCenterTileNonIntegralSize2)
     appendQuads(quadList, sharedStateList, rootLayer.get(), it, occlusionTracker);
     EXPECT_EQ(quadList.size(), 2u);
 
-    EXPECT_NEAR(occlusionTracker.overdrawMetrics().pixelsDrawnOpaque(), 19643, 1);
+    EXPECT_NEAR(occlusionTracker.overdrawMetrics().pixelsDrawnOpaque(), 20000, 1);
     EXPECT_NEAR(occlusionTracker.overdrawMetrics().pixelsDrawnTranslucent(), 0, 1);
     EXPECT_NEAR(occlusionTracker.overdrawMetrics().pixelsCulledForDrawing(), 0, 1);
 }