content: Implement dynamic priorities for raster threads.

cc/raster/task_graph_work_queue.h

Index: cc/raster/task_graph_work_queue.h
diff --git a/cc/raster/task_graph_work_queue.h b/cc/raster/task_graph_work_queue.h
index 0c82f67678a73be42e3424c6c27170ddcc716260..010b847b0c756f60a02da5f5e3e0629f575ee3ae 100644
--- a/cc/raster/task_graph_work_queue.h
+++ b/cc/raster/task_graph_work_queue.h
@@ -16,6 +16,12 @@
 
 namespace cc {
 
+class CC_EXPORT TaskGraphWorkQueueClient {
+  virtual void AdjustWorkerPriorityForTask(Task* task,
+                                           uint16_t old_category,
+                                           uint16_t new_category) = 0;
+};
+
 // Implements a queue of incoming TaskGraph work. Designed for use by
 // implementations of TaskGraphRunner. Not thread safe, so the caller is
 // responsible for all necessary locking.
@@ -70,7 +76,7 @@ class CC_EXPORT TaskGraphWorkQueue {
     std::vector<CategorizedTask> running_tasks;
   };
 
-  TaskGraphWorkQueue();
+  explicit TaskGraphWorkQueue(TaskGraphWorkQueueClient* client);
   virtual ~TaskGraphWorkQueue();
 
   // Gets a NamespaceToken which is guaranteed to be unique within this
@@ -175,6 +181,8 @@ class CC_EXPORT TaskGraphWorkQueue {
     }
   };
 
+  TaskGraphWorkQueueClient* client_;
+
   using TaskNamespaceMap =
       std::map<NamespaceToken, TaskNamespace, CompareToken>;