Revert of cc: Remove WorkerPool class and instead use TaskGraphRunner directly.

cc/resources/worker_pool.h

Index: cc/resources/worker_pool.h
diff --git a/cc/resources/worker_pool.h b/cc/resources/worker_pool.h
new file mode 100644
index 0000000000000000000000000000000000000000..ee095d1336d723127794ee7c3336f21d715c04b8
--- /dev/null
+++ b/cc/resources/worker_pool.h
@@ -0,0 +1,146 @@
+// Copyright 2013 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_RESOURCES_WORKER_POOL_H_
+#define CC_RESOURCES_WORKER_POOL_H_
+
+#include <deque>
+#include <string>
+#include <vector>
+
+#include "base/cancelable_callback.h"
+#include "base/containers/scoped_ptr_hash_map.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/message_loop/message_loop.h"
+#include "cc/base/cc_export.h"
+
+namespace cc {
+namespace internal {
+
+class CC_EXPORT WorkerPoolTask
+    : public base::RefCountedThreadSafe<WorkerPoolTask> {
+ public:
+  virtual void RunOnWorkerThread(unsigned thread_index) = 0;
+  virtual void CompleteOnOriginThread() = 0;
+
+  void DidSchedule();
+  void WillRun();
+  void DidRun();
+  void WillComplete();
+  void DidComplete();
+
+  bool HasFinishedRunning() const;
+  bool HasCompleted() const;
+
+ protected:
+  friend class base::RefCountedThreadSafe<WorkerPoolTask>;
+
+  WorkerPoolTask();
+  virtual ~WorkerPoolTask();
+
+ private:
+  bool did_schedule_;
+  bool did_run_;
+  bool did_complete_;
+};
+
+class CC_EXPORT GraphNode {
+ public:
+  typedef std::vector<GraphNode*> Vector;
+
+  GraphNode(internal::WorkerPoolTask* task, unsigned priority);
+  ~GraphNode();
+
+  WorkerPoolTask* task() { return task_; }
+
+  void add_dependent(GraphNode* dependent) {
+    DCHECK(dependent);
+    dependents_.push_back(dependent);
+  }
+  const Vector& dependents() const { return dependents_; }
+
+  unsigned priority() const { return priority_; }
+
+  unsigned num_dependencies() const { return num_dependencies_; }
+  void add_dependency() { ++num_dependencies_; }
+  void remove_dependency() {
+    DCHECK(num_dependencies_);
+    --num_dependencies_;
+  }
+
+ private:
+  WorkerPoolTask* task_;
+  Vector dependents_;
+  unsigned priority_;
+  unsigned num_dependencies_;
+
+  DISALLOW_COPY_AND_ASSIGN(GraphNode);
+};
+
+}  // namespace internal
+}  // namespace cc
+
+#if defined(COMPILER_GCC)
+namespace BASE_HASH_NAMESPACE {
+template <> struct hash<cc::internal::WorkerPoolTask*> {
+  size_t operator()(cc::internal::WorkerPoolTask* ptr) const {
+    return hash<size_t>()(reinterpret_cast<size_t>(ptr));
+  }
+};
+}  // namespace BASE_HASH_NAMESPACE
+#endif  // COMPILER
+
+namespace cc {
+
+// A worker thread pool that runs tasks provided by task graph and
+// guarantees completion of all pending tasks at shutdown.
+class CC_EXPORT WorkerPool {
+ public:
+  virtual ~WorkerPool();
+
+  // Tells the worker pool to shutdown and returns once all pending tasks have
+  // completed.
+  virtual void Shutdown();
+
+  // Sets the number of threads to use for running raster tasks.
+  // Can only be called once prior to GetNumRasterThreads().
+  // Caller is responsible for correct ordering.
+  // TODO(reveman): Move this to RasterWorkerPool: crbug.com/331844
+  static void SetNumRasterThreads(int num_threads);
+
+  // Gets the number of threads to use for running raster tasks.
+  // TODO(reveman): Move this to RasterWorkerPool: crbug.com/331844
+  static int GetNumRasterThreads();
+
+  // A task graph contains a unique set of tasks with edges between
+  // dependencies pointing in the direction of the dependents. Each task
+  // need to be assigned a unique priority and a run count that matches
+  // the number of dependencies.
+  typedef base::ScopedPtrHashMap<internal::WorkerPoolTask*, internal::GraphNode>
+      GraphNodeMap;
+  typedef GraphNodeMap TaskGraph;
+  typedef std::vector<scoped_refptr<internal::WorkerPoolTask> > TaskVector;
+
+ protected:
+  WorkerPool();
+
+  // Schedule running of tasks in |graph|. Any previously scheduled tasks
+  // that are not already running will be canceled. Canceled tasks don't run
+  // but completion of them is still processed.
+  void SetTaskGraph(TaskGraph* graph);
+
+  // Force a check for completed tasks.
+  void CheckForCompletedWorkerTasks();
+
+ private:
+  void ProcessCompletedTasks(const TaskVector& completed_tasks);
+
+  bool in_dispatch_completion_callbacks_;
+};
+
+}  // namespace cc
+
+#endif  // CC_RESOURCES_WORKER_POOL_H_