Force property_trees rebuild for DamageTrackerTest

cc/trees/damage_tracker_unittest.cc

Index: cc/trees/damage_tracker_unittest.cc
diff --git a/cc/trees/damage_tracker_unittest.cc b/cc/trees/damage_tracker_unittest.cc
index 2df71ddf2a77e287617cdb6f67a0d3f864a40b4c..41ddb7f3692bcb873d95fe73174e4794b4409d49 100644
--- a/cc/trees/damage_tracker_unittest.cc
+++ b/cc/trees/damage_tracker_unittest.cc
@@ -14,6 +14,7 @@
 #include "cc/test/test_shared_bitmap_manager.h"
 #include "cc/test/test_task_graph_runner.h"
 #include "cc/trees/layer_tree_host_common.h"
+#include "cc/trees/layer_tree_impl.h"
 #include "cc/trees/single_thread_proxy.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/skia/include/effects/SkBlurImageFilter.h"
@@ -47,6 +48,7 @@ void ClearDamageForAllSurfaces(LayerImpl* layer) {
 }
 
 void EmulateDrawingOneFrame(LayerImpl* root) {
+  root->layer_tree_impl()->property_trees()->needs_rebuild = true;
   // This emulates only steps that are relevant to testing the damage tracker:
   //   1. computing the render passes and layerlists
   //   2. updating all damage trackers in the correct order