cc: use viewport-wide tiles for GPU rasterization.

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 c1fb010c1bf21c59c36f9f038ae03565f58fe7b8..b68e1d5436d041c5a8d2ed2c3b3827e3dfc3215a 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -644,6 +644,10 @@ bool LayerTreeImpl::device_viewport_valid_for_tile_management() const {
   return layer_tree_host_impl_->device_viewport_valid_for_tile_management();
 }
 
+gfx::Size LayerTreeImpl::device_viewport_size() const {
+  return layer_tree_host_impl_->device_viewport_size();
+}
+
 bool LayerTreeImpl::IsActiveTree() const {
   return layer_tree_host_impl_->active_tree() == this;
 }