Make isolate id getter public.

BUG=
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/17343004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15228 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/isolate.h

@@ -1107,14 +1107,14 @@ class Isolate {
     callback_table_ = callback_table;
   }
 
+  int id() const { return static_cast<int>(id_); }
+
   HStatistics* GetHStatistics();
   HTracer* GetHTracer();
 
  private:
   Isolate();
 
-  int id() const { return static_cast<int>(id_); }
-
   friend struct GlobalState;
   friend struct InitializeGlobalState;