Speculative patch: Make it safe to delete the TQM inside a Task

content/child/scheduler/task_queue_manager.cc

Index: content/child/scheduler/task_queue_manager.cc
diff --git a/content/child/scheduler/task_queue_manager.cc b/content/child/scheduler/task_queue_manager.cc
index 386ebd0c955cc642f6ea09c8db56d004d33e9a41..ccf7743c402d3308e60bb08cd5a29d42bce24c2b 100644
--- a/content/child/scheduler/task_queue_manager.cc
+++ b/content/child/scheduler/task_queue_manager.cc
@@ -464,6 +464,7 @@ TaskQueueManager::TaskQueueManager(
       time_source_(nullptr),
       disabled_by_default_tracing_category_(
           disabled_by_default_tracing_category),
+      deletion_sentinel_(new DeletionSentinel()),
       weak_factory_(this) {
   DCHECK(main_task_runner->RunsTasksOnCurrentThread());
   TRACE_EVENT_OBJECT_CREATED_WITH_ID(disabled_by_default_tracing_category,
@@ -576,6 +577,8 @@ void TaskQueueManager::MaybePostDoWorkOnMainRunner() {
 }
 
 void TaskQueueManager::DoWork(bool posted_from_main_thread) {
+  scoped_refptr<DeletionSentinel> protect(deletion_sentinel_);
+
   if (posted_from_main_thread) {
     pending_dowork_count_--;
     DCHECK_GE(pending_dowork_count_, 0);
@@ -598,6 +601,11 @@ void TaskQueueManager::DoWork(bool posted_from_main_thread) {
     MaybePostDoWorkOnMainRunner();
     ProcessTaskFromWorkQueue(queue_index, i > 0, &previous_task);
 
+    // Detect if the TaskQueueManager got deleted during the

[Sami, 2015/04/08 14:24:04]

This should probably be moved to within ProcessTaskFromWorkQueue so that we bail
out immediately after the task runs. Actually |protect| could also be moved
there.

[alex clarke (OOO till 29th), 2015/04/08 14:33:05]

Done.

+    // ProcessTaskFromWorkQueue call.
+    if (protect->HasOneRef())
+      return;
+
     if (!UpdateWorkQueues(&previous_task))
       return;
   }