Reland - Refactor signaling in RWP

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 95d3c772c24f22ea478757e2d1a81d40ab231b9e..7fbd19b714243b0a379197f675449583cc79e453 100644
--- a/cc/raster/task_graph_work_queue.h
+++ b/cc/raster/task_graph_work_queue.h
@@ -46,6 +46,8 @@ class CC_EXPORT TaskGraphWorkQueue {
     uint16_t priority;
   };
 
+  using CategorizedTask = std::pair<uint16_t, scoped_refptr<Task>>;
+
   // Helper classes and static methods used by dependent classes.
   struct TaskNamespace {
     typedef std::vector<TaskNamespace*> Vector;
@@ -64,7 +66,7 @@ class CC_EXPORT TaskGraphWorkQueue {
     Task::Vector completed_tasks;
 
     // This set contains all currently running tasks.
-    Task::Vector running_tasks;
+    std::vector<CategorizedTask> running_tasks;
   };
 
   TaskGraphWorkQueue();
@@ -145,6 +147,19 @@ class CC_EXPORT TaskGraphWorkQueue {
     return ready_to_run_namespaces_;
   }
 
+  size_t NumRunningTasksForCategory(uint16_t category) const {
+    size_t count = 0;
+    for (const auto& task_namespace_entry : namespaces_) {
+      for (const auto& categorized_task :
+           task_namespace_entry.second.running_tasks) {
+        if (categorized_task.first == category) {
+          ++count;
+        }
+      }
+    }
+    return count;
+  }
+
   // Helper function which ensures that graph dependencies were correctly
   // configured.
   static bool DependencyMismatch(const TaskGraph* graph);