Fixed example in MessageLoop::ReleaseSoon comment

The previous version could cause race condition if for whatever reason ReleaseSoon finished releasing on another thread before we got to "foo = NULL"

BUG=

Review URL: https://codereview.chromium.org/301943003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@273879 0039d316-1c4b-4281-b951-d872f2087c98

base/message_loop/message_loop.h

@@ -208,15 +208,16 @@ class BASE_EXPORT MessageLoop : public MessagePump::Delegate {
   // 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
+  // (AddRef), clear the pointer, then issue a ReleaseSoon.  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->AddRef();
+  // Foo* raw_foo = foo.get();
   // foo = NULL;
+  // message_loop->ReleaseSoon(raw_foo);
   //
   // NOTE: This method may be called on any thread.  The object will be
   // released (and thus possibly deleted) on the thread that executes