cc: Split Proxy to eliminate unnecessary dependencies on the impl side

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index dda446a8ee9ceceded6a3aaf5f3d66be01f2fc74..617bebecb4474e8f86f0a4c978b5d12caff9b884 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -732,10 +732,9 @@ bool LayerTreeImpl::UpdateDrawProperties(bool update_lcd_text) {
   // raster source due to draw properties.
   if (update_lcd_text) {
     // TODO(enne): Make LTHI::sync_tree return this value.
-    LayerTreeImpl* sync_tree =
-        layer_tree_host_impl_->proxy()->CommitToActiveTree()
-            ? layer_tree_host_impl_->active_tree()
-            : layer_tree_host_impl_->pending_tree();
+    LayerTreeImpl* sync_tree = layer_tree_host_impl_->CommitToActiveTree()
+                                   ? layer_tree_host_impl_->active_tree()
+                                   : layer_tree_host_impl_->pending_tree();
     // If this is not the sync tree, then it is not safe to update lcd text
     // as it causes invalidations and the tiles may be in use.
     DCHECK_EQ(this, sync_tree);
@@ -875,8 +874,8 @@ void LayerTreeImpl::ResetViewportSizeInvalid() {
   layer_tree_host_impl_->OnCanDrawStateChangedForTree();
 }
 
-Proxy* LayerTreeImpl::proxy() const {
-  return layer_tree_host_impl_->proxy();
+ThreadVerifier* LayerTreeImpl::thread_verifier() const {
+  return layer_tree_host_impl_->thread_verifier();
 }
 
 const LayerTreeSettings& LayerTreeImpl::settings() const {
@@ -1657,7 +1656,7 @@ bool LayerTreeImpl::SmoothnessTakesPriority() const {
 }
 
 BlockingTaskRunner* LayerTreeImpl::BlockingMainThreadTaskRunner() const {
-  return proxy()->blocking_main_thread_task_runner();
+  return thread_verifier()->blocking_main_thread_task_runner();
 }
 
 VideoFrameControllerClient* LayerTreeImpl::GetVideoFrameControllerClient()