Re-land: cc: Add raster finished signals to RasterWorkerPool.

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
index 57bc774c082b8d19307f30e4876f1cba54d0f4b8..06cbf089401da4476f6307a9f05efaf88149d026 100644
--- a/cc/resources/worker_pool.h
+++ b/cc/resources/worker_pool.h
@@ -80,10 +80,9 @@ class CC_EXPORT WorkerPool {
    public:
     typedef std::vector<GraphNode*> Vector;
 
-    GraphNode();
+    GraphNode(internal::WorkerPoolTask* task, unsigned priority);
     ~GraphNode();
 
-    void set_task(internal::WorkerPoolTask* task) { task_ = task; }
     internal::WorkerPoolTask* task() { return task_; }
 
     void add_dependent(GraphNode* dependent) {
@@ -94,7 +93,6 @@ class CC_EXPORT WorkerPool {
       return dependents_;
     }
 
-    void set_priority(unsigned priority) { priority_ = priority; }
     unsigned priority() const { return priority_; }
 
     unsigned num_dependencies() const {