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

cc/resources/pixel_buffer_raster_worker_pool.cc

Index: cc/resources/pixel_buffer_raster_worker_pool.cc
diff --git a/cc/resources/pixel_buffer_raster_worker_pool.cc b/cc/resources/pixel_buffer_raster_worker_pool.cc
index e32176bf7b0e7d8a679f6c3d3a42e90cc07e5d78..33eaf34d1d0d91301c6e3af63ed3237653768df2 100644
--- a/cc/resources/pixel_buffer_raster_worker_pool.cc
+++ b/cc/resources/pixel_buffer_raster_worker_pool.cc
@@ -32,7 +32,7 @@
         needs_upload_(false) {
   }
 
-  // Overridden from internal::Task:
+  // Overridden from internal::WorkerPoolTask:
   virtual void RunOnWorkerThread(unsigned thread_index) OVERRIDE {
     // |buffer_| can be NULL in lost context situations.
     if (!buffer_) {
@@ -46,8 +46,6 @@
                                              task_->resource()->size(),
                                              0);
   }
-
-  // Overridden from internal::WorkerPoolTask:
   virtual void CompleteOnOriginThread() OVERRIDE {
     // |needs_upload_| must be be false if task didn't run.
     DCHECK(HasFinishedRunning() || !needs_upload_);
@@ -120,8 +118,7 @@
 void PixelBufferRasterWorkerPool::Shutdown() {
   shutdown_ = true;
   RasterWorkerPool::Shutdown();
-
-  CheckForCompletedWorkerPoolTasks();
+  CheckForCompletedWorkerTasks();
   CheckForCompletedUploads();
   check_for_completed_raster_tasks_callback_.Cancel();
   check_for_completed_raster_tasks_pending_ = false;
@@ -210,7 +207,7 @@
   // Check for completed tasks when ScheduleTasks() is called as
   // priorities might have changed and this maximizes the number
   // of top priority tasks that are scheduled.
-  CheckForCompletedWorkerPoolTasks();
+  CheckForCompletedWorkerTasks();
   CheckForCompletedUploads();
   FlushUploads();
 
@@ -230,7 +227,7 @@
       "state", TracedValue::FromValue(StateAsValue().release()));
 }
 
-unsigned PixelBufferRasterWorkerPool::GetResourceTarget() const {
+GLenum PixelBufferRasterWorkerPool::GetResourceTarget() const {
   return GL_TEXTURE_2D;
 }
 
@@ -394,7 +391,7 @@
   check_for_completed_raster_tasks_callback_.Cancel();
   check_for_completed_raster_tasks_pending_ = false;
 
-  CheckForCompletedWorkerPoolTasks();
+  CheckForCompletedWorkerTasks();
   CheckForCompletedUploads();
   FlushUploads();