cc: Avoid ResourceProvider nullptr deref

cc/trees/layer_tree_host_impl.h

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_TREES_LAYER_TREE_HOST_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include <stddef.h>
 
 #include <bitset>
@@ skipping 820 matching lines @@
   SharedBitmapManager* shared_bitmap_manager_;
   gpu::GpuMemoryBufferManager* gpu_memory_buffer_manager_;
   TaskGraphRunner* task_graph_runner_;
   int id_;
 
   std::set<SwapPromiseMonitor*> swap_promise_monitor_;
 
   bool requires_high_res_to_draw_;
   bool is_likely_to_require_a_draw_;
 
+  // TODO(danakj): Delete the compositor frame sink and all resources when
+  // it's lost instead of having this bool.
+  bool has_valid_compositor_frame_sink_;
+
   std::unique_ptr<Viewport> viewport_;
 
   std::unique_ptr<LayerTreeMutator> mutator_;
 
   std::unique_ptr<PendingTreeDurationHistogramTimer>
       pending_tree_duration_timer_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_