Adding TryPostTask to the message loop

base/message_loop.h

Index: base/message_loop.h
diff --git a/base/message_loop.h b/base/message_loop.h
index dbe75a57f9f410ae1a672745c1daffdb8ee4ce37..070fd2cc4d91c2c4c93e87575cea0886636464b8 100644
--- a/base/message_loop.h
+++ b/base/message_loop.h
@@ -168,12 +168,20 @@ class BASE_EXPORT MessageLoop : public base::MessagePump::Delegate {
   // PostTask(from_here, task) is equivalent to
   // PostDelayedTask(from_here, task, 0).
   //
+  // The TryPostTask is meant for the cases where the calling thread cannot
+  // block. If posting the task will block, the call returns false, the task
+  // is not posted but the task is consumed anyways.
+  //
   // NOTE: These methods may be called on any thread.  The Task will be invoked
   // on the thread that executes MessageLoop::Run().
   void PostTask(
       const tracked_objects::Location& from_here,
       const base::Closure& task);
 
+  bool TryPostTask(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task);
+
   void PostDelayedTask(
       const tracked_objects::Location& from_here,
       const base::Closure& task,
@@ -437,7 +445,11 @@ class BASE_EXPORT MessageLoop : public base::MessagePump::Delegate {
   // reset the value of pending_task->task.  This is needed to ensure
   // that the posting call stack does not retain pending_task->task
   // beyond this function call.
-  void AddToIncomingQueue(base::PendingTask* pending_task);
+  // If |use_try_lock| is true, The function fails if another thread is
+  // queuing or dequeing at that moment. In that case the function returns
+  // false. If |use_try_lock| is false there is no need to check the
+  // return value.
+  bool AddToIncomingQueue(base::PendingTask* pending_task, bool use_try_lock);
 
   // Load tasks from the incoming_queue_ into work_queue_ if the latter is
   // empty.  The former requires a lock to access, while the latter is directly