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

cc/tiled_layer_impl_unittest.cc

Index: cc/tiled_layer_impl_unittest.cc
diff --git a/cc/tiled_layer_impl_unittest.cc b/cc/tiled_layer_impl_unittest.cc
index 257b07c7b6fa177ced2a4974fd3deb29047b8f5c..4a7403b65d4fa46270f2f32e26cffe16bd3df2b3 100644
--- a/cc/tiled_layer_impl_unittest.cc
+++ b/cc/tiled_layer_impl_unittest.cc
@@ -110,7 +110,7 @@ TEST(TiledLayerImplTest, checkerboarding)
         AppendQuadsData data;
         layer->appendQuads(quadCuller, data);
         EXPECT_EQ(quadCuller.quadList().size(), 4u);
-        EXPECT_FALSE(data.hadMissingTiles);
+        EXPECT_EQ(0u, data.numMissingTiles);
 
         for (size_t i = 0; i < quadCuller.quadList().size(); ++i)
             EXPECT_EQ(quadCuller.quadList()[i]->material, DrawQuad::TILED_CONTENT);
@@ -125,7 +125,7 @@ TEST(TiledLayerImplTest, checkerboarding)
         MockQuadCuller quadCuller;
         AppendQuadsData data;
         layer->appendQuads(quadCuller, data);
-        EXPECT_TRUE(data.hadMissingTiles);
+        EXPECT_LT(0u, data.numMissingTiles);
         EXPECT_EQ(quadCuller.quadList().size(), 4u);
         for (size_t i = 0; i < quadCuller.quadList().size(); ++i)
             EXPECT_NE(quadCuller.quadList()[i]->material, DrawQuad::TILED_CONTENT);