Force events to be non blocking if main thread is unresponsive.

third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc

Index: third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc
diff --git a/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc b/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc
index 0ebf0ab05dbc9b287384c6ef5b41bd3683e7e720..dabe30ae8cf37d2be9070c136f7b2f5474a2a99f 100644
--- a/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc
+++ b/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc
@@ -247,9 +247,20 @@ void TaskQueueManager::DoWork(base::TimeTicks run_time, bool from_main_thread) {
     // when we are in DoWork (but WorkQueue may be deleted).
     internal::TaskQueueImpl* task_queue = work_queue->task_queue();
 
+    if (!delegate_->IsNested()) {
+      for (auto& observer : task_time_observers_)
+        observer.ReportTaskStartTime(MonotonicTimeInSeconds(task_start_time));
+    }
+
     switch (ProcessTaskFromWorkQueue(work_queue)) {
       case ProcessTaskResult::DEFERRED:
+        // TODO - test this case.
         // If a task was deferred, try again with another task.
+        for (auto& observer : task_time_observers_) {
+          observer.ReportTaskEndTime(task_queue,
+                                     MonotonicTimeInSeconds(task_start_time),
+                                     MonotonicTimeInSeconds(task_start_time));
+        }
         continue;
       case ProcessTaskResult::EXECUTED:
         break;
@@ -262,9 +273,9 @@ void TaskQueueManager::DoWork(base::TimeTicks run_time, bool from_main_thread) {
       // Only report top level task durations.
       base::TimeTicks task_end_time = lazy_now.Now();
       for (auto& observer : task_time_observers_) {
-        observer.ReportTaskTime(task_queue,
-                                MonotonicTimeInSeconds(task_start_time),
-                                MonotonicTimeInSeconds(task_end_time));
+        observer.ReportTaskEndTime(task_queue,
+                                   MonotonicTimeInSeconds(task_start_time),
+                                   MonotonicTimeInSeconds(task_end_time));
       }
       task_start_time = task_end_time;
     }