content: Add heartbeat trace for CategorizedWorkerPool.

content/renderer/categorized_worker_pool.h

Index: content/renderer/categorized_worker_pool.h
diff --git a/content/renderer/categorized_worker_pool.h b/content/renderer/categorized_worker_pool.h
index 2f75f2183f24d0c145e55697f53c86470f371837..cbfd74b9028b8e6df1d242d235c4328e3ea64215 100644
--- a/content/renderer/categorized_worker_pool.h
+++ b/content/renderer/categorized_worker_pool.h
@@ -116,6 +116,10 @@ class CONTENT_EXPORT CategorizedWorkerPool : public base::TaskRunner,
   // low enough to start a new one.
   bool ShouldRunTaskForCategoryWithLockAcquired(cc::TaskCategory category);
 
+  // Wait for more tasks to run on the given thread.
+  void WaitForMoreTasksWithLockAcquired(
+      base::ConditionVariable* has_ready_to_run_tasks_cv);
+
   // The actual threads where work is done.
   std::vector<std::unique_ptr<base::SimpleThread>> threads_;