Lazily initialize MessageLoop for faster thread startup

base/message_loop/incoming_task_queue.cc

Index: base/message_loop/incoming_task_queue.cc
diff --git a/base/message_loop/incoming_task_queue.cc b/base/message_loop/incoming_task_queue.cc
index c1ce939b0c4708ac431d80b54a35ee8ef73b314c..d3dff86751930efa0aed4b0d4dcd050326261d0e 100644
--- a/base/message_loop/incoming_task_queue.cc
+++ b/base/message_loop/incoming_task_queue.cc
@@ -47,6 +47,14 @@ IncomingTaskQueue::IncomingTaskQueue(MessageLoop* message_loop)
       always_schedule_work_(AlwaysNotifyPump(message_loop_->type())) {
 }
 
+// static
+IncomingTaskQueue* IncomingTaskQueue::CreateForLazyInitMessageLoop(
+    MessageLoop* message_loop) {
+  IncomingTaskQueue* queue = new IncomingTaskQueue(message_loop);
+  queue->message_loop_not_initialized_ = true;
+  return queue;
+}
+
 bool IncomingTaskQueue::AddToIncomingQueue(
     const tracked_objects::Location& from_here,
     const Closure& task,
@@ -109,6 +117,21 @@ void IncomingTaskQueue::WillDestroyCurrentMessageLoop() {
   message_loop_ = NULL;
 }
 
+void IncomingTaskQueue::DidInitializeMessageLoop() {
+  AutoLock lock(incoming_queue_lock_);
+  DCHECK(message_loop_not_initialized_);
+  message_loop_not_initialized_ = false;
+  if (!incoming_queue_.empty()) {
+    message_loop_->ScheduleWork();
+    message_loop_scheduled_ = true;
+  }
+}
+
+bool IncomingTaskQueue::empty() {
+  AutoLock lock(incoming_queue_lock_);
+  return incoming_queue_.empty();
+}
+
 IncomingTaskQueue::~IncomingTaskQueue() {
   // Verify that WillDestroyCurrentMessageLoop() has been called.
   DCHECK(!message_loop_);
@@ -148,7 +171,8 @@ bool IncomingTaskQueue::PostPendingTask(PendingTask* pending_task) {
   incoming_queue_.push(*pending_task);
   pending_task->task.Reset();
 
-  if (always_schedule_work_ || (!message_loop_scheduled_ && was_empty)) {
+  if (!message_loop_not_initialized_ &&
+      (always_schedule_work_ || (!message_loop_scheduled_ && was_empty))) {
     // Wake up the message loop.
     message_loop_->ScheduleWork();
     // After we've scheduled the message loop, we do not need to do so again