ppapi: fix outdated comment in cpp header.

TBR=brettw
(LGTM'ed under http://codereview.chromium.org/7616014/)

BUG=none
TEST=n/a
Review URL: http://codereview.chromium.org/7634005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@96536 0039d316-1c4b-4281-b951-d872f2087c98

ppapi/cpp/completion_callback.h

@@ -193,8 +193,7 @@ class CompletionCallbackFactory {
   // CompletionCallback to a PPAPI method, the method does not return
   // PP_OK_COMPLETIONPENDING, then you should manually call the
   // CompletionCallback's Run method, or memory will be leaked.
-  // NewCallback() is equivalent to NewOptionalCallback().
-  // TODO(polina): update this comment when this is no longer true.
+  // NewCallback() is equivalent to NewRequiredCallback().
 
   template <typename Method>
   CompletionCallback NewCallback(Method method) {