Reland - Refactor signaling in RWP

cc/raster/task_graph_work_queue.cc

Index: cc/raster/task_graph_work_queue.cc
diff --git a/cc/raster/task_graph_work_queue.cc b/cc/raster/task_graph_work_queue.cc
index 87800576dd5177b9e4f2bba196a550c6b8e27c7e..a36426ad2f0e85fe61943d01c584d15879e2b800 100644
--- a/cc/raster/task_graph_work_queue.cc
+++ b/cc/raster/task_graph_work_queue.cc
@@ -195,6 +195,7 @@ TaskGraphWorkQueue::PrioritizedTask TaskGraphWorkQueue::GetNextTaskToRun(
 
   // Add task to |running_tasks|.
   task_namespace->running_tasks.push_back(task.task);
+  running_task_count_[category]++;
 
   return task;
 }
@@ -209,6 +210,7 @@ void TaskGraphWorkQueue::CompleteTask(const PrioritizedTask& completed_task) {
   DCHECK(it != task_namespace->running_tasks.end());
   std::swap(*it, task_namespace->running_tasks.back());
   task_namespace->running_tasks.pop_back();
+  running_task_count_[completed_task.category]--;
 
   // Now iterate over all dependents to decrement dependencies and check if they
   // are ready to run.