Automated IWYU fix for TaskRunner includes.

cc/trees/layer_tree_host.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_H_
 #define CC_TREES_LAYER_TREE_HOST_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <limits>
 #include <memory>
 #include <set>
 #include <string>
 #include <unordered_map>
 #include <vector>
 
 #include "base/cancelable_callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
+#include "base/single_thread_task_runner.h"
 #include "base/time/time.h"
 #include "cc/benchmarks/micro_benchmark.h"
 #include "cc/benchmarks/micro_benchmark_controller.h"
 #include "cc/cc_export.h"
 #include "cc/input/browser_controls_state.h"
 #include "cc/input/event_listener_properties.h"
 #include "cc/input/input_handler.h"
 #include "cc/input/layer_selection_bound.h"
 #include "cc/input/scrollbar.h"
 #include "cc/layers/layer_collections.h"
@@ skipping 592 matching lines @@
 
   std::vector<std::pair<sk_sp<const SkImage>, base::Callback<void(bool)>>>
       queued_image_decodes_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHost);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_H_