cc : Add DCHECKs to ensure we have valid proprety tree indices at commit

cc/trees/tree_synchronizer_unittest.cc

Index: cc/trees/tree_synchronizer_unittest.cc
diff --git a/cc/trees/tree_synchronizer_unittest.cc b/cc/trees/tree_synchronizer_unittest.cc
index cbae4e4aea1ba7de93a2f9b7ebe95a587f99a1d5..f06a4ad22d78cfef8ab75523c5f5319a1e85ec54 100644
--- a/cc/trees/tree_synchronizer_unittest.cc
+++ b/cc/trees/tree_synchronizer_unittest.cc
@@ -165,6 +165,7 @@ TEST_F(TreeSynchronizerTest, SyncSimpleTreeFromEmpty) {
   layer_tree_root->AddChild(Layer::Create());
 
   host_->SetRootLayer(layer_tree_root);
+  host_->BuildPropertyTreesForTesting();
 
   TreeSynchronizer::SynchronizeTrees(layer_tree_root.get(),
                                      host_->active_tree());
@@ -186,6 +187,7 @@ TEST_F(TreeSynchronizerTest, SyncSimpleTreeReusingLayers) {
   int second_layer_impl_id = layer_tree_root->children()[1]->id();
 
   host_->SetRootLayer(layer_tree_root);
+  host_->BuildPropertyTreesForTesting();
 
   TreeSynchronizer::SynchronizeTrees(layer_tree_root.get(),
                                      host_->active_tree());
@@ -206,6 +208,7 @@ TEST_F(TreeSynchronizerTest, SyncSimpleTreeReusingLayers) {
 
   // Synchronize again. After the sync the trees should be equivalent and we
   // should have created and destroyed one LayerImpl.
+  host_->BuildPropertyTreesForTesting();
   TreeSynchronizer::SynchronizeTrees(layer_tree_root.get(),
                                      host_->active_tree());
   layer_impl_tree_root = host_->active_tree()->root_layer_for_testing();
@@ -236,6 +239,7 @@ TEST_F(TreeSynchronizerTest, SyncSimpleTreeAndTrackStackingOrderChange) {
 
   host_->SetRootLayer(layer_tree_root);
 
+  host_->BuildPropertyTreesForTesting();
   TreeSynchronizer::SynchronizeTrees(layer_tree_root.get(),
                                      host_->active_tree());
   LayerImpl* layer_impl_tree_root =
@@ -252,12 +256,15 @@ TEST_F(TreeSynchronizerTest, SyncSimpleTreeAndTrackStackingOrderChange) {
   // re-insert the layer and sync again.
   child2->RemoveFromParent();
   layer_tree_root->AddChild(child2);
+  host_->BuildPropertyTreesForTesting();
   TreeSynchronizer::SynchronizeTrees(layer_tree_root.get(),
                                      host_->active_tree());
   layer_impl_tree_root = host_->active_tree()->root_layer_for_testing();
   ExpectTreesAreIdentical(layer_tree_root.get(), layer_impl_tree_root,
                           host_->active_tree());
 
+  host_->active_tree()->SetPropertyTrees(
+      layer_tree_root->layer_tree_host()->property_trees());
   TreeSynchronizer::PushLayerProperties(layer_tree_root->layer_tree_host(),
                                         host_->active_tree());
 
@@ -287,6 +294,7 @@ TEST_F(TreeSynchronizerTest, SyncSimpleTreeAndProperties) {
   layer_tree_root->children()[1]->SavePaintProperties();
   int second_child_id = layer_tree_root->children()[1]->id();
 
+  host_->BuildPropertyTreesForTesting();
   TreeSynchronizer::SynchronizeTrees(layer_tree_root.get(),
                                      host_->active_tree());
   LayerImpl* layer_impl_tree_root =
@@ -335,6 +343,7 @@ TEST_F(TreeSynchronizerTest, ReuseLayerImplsAfterStructuralChange) {
   scoped_refptr<Layer> layer_d = layer_b->children()[1];
 
   host_->SetRootLayer(layer_tree_root);
+  host_->BuildPropertyTreesForTesting();
 
   TreeSynchronizer::SynchronizeTrees(layer_tree_root.get(),
                                      host_->active_tree());
@@ -363,6 +372,7 @@ TEST_F(TreeSynchronizerTest, ReuseLayerImplsAfterStructuralChange) {
 
   // After another synchronize our trees should match and we should not have
   // destroyed any LayerImpls
+  host_->BuildPropertyTreesForTesting();
   TreeSynchronizer::SynchronizeTrees(layer_tree_root.get(),
                                      host_->active_tree());
   layer_impl_tree_root = host_->active_tree()->root_layer_for_testing();
@@ -392,6 +402,7 @@ TEST_F(TreeSynchronizerTest, SyncSimpleTreeThenDestroy) {
   int old_tree_first_child_layer_id = old_layer_tree_root->children()[0]->id();
   int old_tree_second_child_layer_id = old_layer_tree_root->children()[1]->id();
 
+  host_->BuildPropertyTreesForTesting();
   TreeSynchronizer::SynchronizeTrees(old_layer_tree_root.get(),
                                      host_->active_tree());
   LayerImpl* layer_impl_tree_root =
@@ -411,6 +422,7 @@ TEST_F(TreeSynchronizerTest, SyncSimpleTreeThenDestroy) {
   scoped_refptr<Layer> new_layer_tree_root = Layer::Create();
   host_->SetRootLayer(new_layer_tree_root);
 
+  host_->BuildPropertyTreesForTesting();
   TreeSynchronizer::SynchronizeTrees(new_layer_tree_root.get(),
                                      host_->active_tree());
   layer_impl_tree_root = host_->active_tree()->root_layer_for_testing();