Add a stat to the smoothness benchmark for avg number of missing tiles.

cc/picture_layer_impl.cc

Index: cc/picture_layer_impl.cc
diff --git a/cc/picture_layer_impl.cc b/cc/picture_layer_impl.cc
index 9a9c0434b21da1ad53ca55fca591b9d2ed3970c1..f73f98504a79a249e896070175d89e88711cffb0 100644
--- a/cc/picture_layer_impl.cc
+++ b/cc/picture_layer_impl.cc
@@ -86,13 +86,13 @@ void PictureLayerImpl::appendQuads(QuadSink& quadSink,
         scoped_ptr<CheckerboardDrawQuad> quad = CheckerboardDrawQuad::Create();
         SkColor color = DebugColors::DefaultCheckerboardColor();
         quad->SetNew(sharedQuadState, geometry_rect, color);
-        appendQuadsData.hadMissingTiles |=
-            quadSink.append(quad.PassAs<DrawQuad>(), appendQuadsData);
+        if (quadSink.append(quad.PassAs<DrawQuad>(), appendQuadsData))
+            appendQuadsData.numMissingTiles++;
       } else {
         scoped_ptr<SolidColorDrawQuad> quad = SolidColorDrawQuad::Create();
         quad->SetNew(sharedQuadState, geometry_rect, backgroundColor());
-        appendQuadsData.hadMissingTiles |=
-            quadSink.append(quad.PassAs<DrawQuad>(), appendQuadsData);
+        if (quadSink.append(quad.PassAs<DrawQuad>(), appendQuadsData))
+            appendQuadsData.numMissingTiles++;
       }
       continue;
     }