Implementation of PostTaskAndReply() in MessageLoopProxy and BrowserThread.

base/message_loop_proxy.h

Index: base/message_loop_proxy.h
diff --git a/base/message_loop_proxy.h b/base/message_loop_proxy.h
index 646b2efcbcc86bb8559c3e2d130499a35652cbb5..4f83d0d53faff3aac13a8b193005ba9e09207a45 100644
--- a/base/message_loop_proxy.h
+++ b/base/message_loop_proxy.h
@@ -67,6 +67,24 @@ class BASE_EXPORT MessageLoopProxy
   // this proxy represents.
   virtual bool BelongsToCurrentThread() = 0;
 
+  // Executes |task| on the given MessageLoopProxy.  On completion, |reply|
+  // is passed back to the MessageLoopProxy for the thread that called
+  // PostTaskAndReply().
+  //
+  // Both |task| and |reply| are guaranteed to be deleted on the thread from
+  // which PostTaskAndReply() is invoked.
+  //
+  // This simplifies logic when an operation needs to be executed on another
+  // thread, but processing of the result needs to occur on the current thread.
+  //
+  // Note that because of the lifetime guarantees on the |reply| Closure, it is
+  // perfectly valid to use a WeakPtr<> in the bound parameters for |reply|.
+  // This is useful if |reply| needs to be canceled on the originating thread
+  // while |task| may still be executing.
+  bool PostTaskAndReply(const tracked_objects::Location& from_here,
+                        const Closure& task,
+                        const Closure& reply);
+
   template <class T>
   bool DeleteSoon(const tracked_objects::Location& from_here,
                   T* object) {