cc: Add an integration test for what scale we draw with after pinching

cc/test/layer_tree_test.cc

Index: cc/test/layer_tree_test.cc
diff --git a/cc/test/layer_tree_test.cc b/cc/test/layer_tree_test.cc
index 8be75bd8df048aed1e0460c8735f9596290d38e5..519052fce776f72bbfec498550e38cf387dc365e 100644
--- a/cc/test/layer_tree_test.cc
+++ b/cc/test/layer_tree_test.cc
@@ -256,6 +256,11 @@ class LayerTreeHostImplForTesting : public LayerTreeHostImpl {
     return test_hooks_->LowFrequencyAnimationInterval();
   }
 
+  void NotifyTileStateChanged(const Tile* tile) override {
+    LayerTreeHostImpl::NotifyTileStateChanged(tile);
+    test_hooks_->NotifyTileStateChangedOnThread(this, tile);
+  }
+
  private:
   TestHooks* test_hooks_;
   bool block_notify_ready_to_activate_for_testing_;