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

cc/resources/image_raster_worker_pool.cc

Index: cc/resources/image_raster_worker_pool.cc
diff --git a/cc/resources/image_raster_worker_pool.cc b/cc/resources/image_raster_worker_pool.cc
index 4520d2223c32e135f00af76aea9cefda84977659..e842970962efc68c3f6d2d140fec0884355f3f5b 100644
--- a/cc/resources/image_raster_worker_pool.cc
+++ b/cc/resources/image_raster_worker_pool.cc
@@ -28,7 +28,7 @@
         reply_(reply) {
   }
 
-  // Overridden from internal::Task:
+  // Overridden from internal::WorkerPoolTask:
   virtual void RunOnWorkerThread(unsigned thread_index) OVERRIDE {
     TRACE_EVENT0("cc", "ImageWorkerPoolTaskImpl::RunOnWorkerThread");
     if (!buffer_)
@@ -39,8 +39,6 @@
                              task_->resource()->size(),
                              stride_);
   }
-
-  // Overridden from internal::WorkerPoolTask:
   virtual void CompleteOnOriginThread() OVERRIDE {
     reply_.Run(!HasFinishedRunning());
   }
@@ -61,7 +59,7 @@
 ImageRasterWorkerPool::ImageRasterWorkerPool(
     ResourceProvider* resource_provider,
     ContextProvider* context_provider,
-    unsigned texture_target)
+    GLenum texture_target)
     : RasterWorkerPool(resource_provider, context_provider),
       texture_target_(texture_target),
       raster_tasks_pending_(false),
@@ -169,7 +167,7 @@
       "state", TracedValue::FromValue(StateAsValue().release()));
 }
 
-unsigned ImageRasterWorkerPool::GetResourceTarget() const {
+GLenum ImageRasterWorkerPool::GetResourceTarget() const {
   return texture_target_;
 }
 
@@ -225,7 +223,7 @@
 // static
 void ImageRasterWorkerPool::CreateGraphNodeForImageTask(
     internal::WorkerPoolTask* image_task,
-    const internal::Task::Vector& decode_tasks,
+    const TaskVector& decode_tasks,
     unsigned priority,
     bool is_required_for_activation,
     internal::GraphNode* raster_required_for_activation_finished_node,