content: Add heartbeat trace for CategorizedWorkerPool.

content/renderer/categorized_worker_pool.cc

Index: content/renderer/categorized_worker_pool.cc
diff --git a/content/renderer/categorized_worker_pool.cc b/content/renderer/categorized_worker_pool.cc
index 41814b4bcd324b2c0f2af1d20b45cc570a4afb35..5806284c0f1a40b423083f5b00acf9003e2acac1 100644
--- a/content/renderer/categorized_worker_pool.cc
+++ b/content/renderer/categorized_worker_pool.cc
@@ -17,6 +17,8 @@
 namespace content {
 namespace {
 
+constexpr int kHeartbeatIntervalInSeconds = 60;  // 1 minute
+
 // A thread which forwards to CategorizedWorkerPool::Run with the runnable
 // categories.
 class CategorizedWorkerPoolThread : public base::SimpleThread {
@@ -239,12 +241,23 @@ void CategorizedWorkerPool::Run(
         break;
 
       // Wait for more tasks.
-      has_ready_to_run_tasks_cv->Wait();
+      WaitForMoreTasksWithLockAcquired(has_ready_to_run_tasks_cv);
       continue;
     }
   }
 }
 
+void CategorizedWorkerPool::WaitForMoreTasksWithLockAcquired(
+    base::ConditionVariable* has_ready_to_run_tasks_cv) {
+  const base::TimeDelta timeout =
+      base::TimeDelta::FromSeconds(kHeartbeatIntervalInSeconds);
+  while (has_ready_to_run_tasks_cv->TimedWait(timeout)) {
+    TRACE_EVENT_INSTANT0(
+        "heartbeat", "CategorizedWorkerPool::HeartbeatDuringWaitForMoreTasks",
+        TRACE_EVENT_SCOPE_THREAD);
+  }
+}
+
 void CategorizedWorkerPool::FlushForTesting() {
   base::AutoLock lock(lock_);