Add example to MessageLoop::ReleaseSoon comment.

base/message_loop/message_loop.h

Index: base/message_loop/message_loop.h
diff --git a/base/message_loop/message_loop.h b/base/message_loop/message_loop.h
index 4bb7d550bccf53a53c062daea1436208bd6e6b38..25891c5dc7c7c4866a5b865b8b1cc13f9092daaa 100644
--- a/base/message_loop/message_loop.h
+++ b/base/message_loop/message_loop.h
@@ -207,6 +207,17 @@ class BASE_EXPORT MessageLoop : public MessagePump::Delegate {
   // live until the next run of the MessageLoop, or if the object needs to be
   // released on a particular thread.
   //
+  // A common pattern is to manually increment the object's reference count
+  // (AddRef), issue a ReleaseSoon, then clear the pointer.  The reference count
+  // is incremented manually to ensure clearing the pointer does not trigger a
+  // delete and to account for the upcoming decrement (ReleaseSoon).  For
+  // example:
+  //
+  // scoped_refptr<Foo> foo = ...
+  // foo.AddRef();
+  // message_loop->ReleaseSoon(foo.get());
+  // foo = NULL;
+  //
   // NOTE: This method may be called on any thread.  The object will be
   // released (and thus possibly deleted) on the thread that executes
   // MessageLoop::Run().  If this is not the same as the thread that calls