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..93cadc8d789f1c9229ffe18792b397c55af08112 100644
--- a/cc/raster/task_graph_work_queue.h
+++ b/cc/raster/task_graph_work_queue.h
@@ -60,11 +60,11 @@ class CC_EXPORT TaskGraphWorkQueue {
     // category.
     std::map<uint16_t, PrioritizedTask::Vector> ready_to_run_tasks;
 
+    // This set contains all currently running tasks.
+    std::map<uint16_t, Task::Vector> running_tasks;
+
     // Completed tasks not yet collected by origin thread.
     Task::Vector completed_tasks;
-
-    // This set contains all currently running tasks.
-    Task::Vector running_tasks;
   };
 
   TaskGraphWorkQueue();
@@ -145,6 +145,18 @@ 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_) {
+      const auto& running_tasks = task_namespace_entry.second.running_tasks;
+      const auto& running_tasks_for_category = running_tasks.find(category);
+      if (running_tasks_for_category != running_tasks.cend()) {
+        count += running_tasks_for_category->second.size();
+      }
+    }
+    return count;
+  }
+
   // Helper function which ensures that graph dependencies were correctly
   // configured.
   static bool DependencyMismatch(const TaskGraph* graph);