Create frequently used symbols in the vm isolate

vm/isolate.h

Index: vm/isolate.h
===================================================================
--- vm/isolate.h	(revision 9729)
+++ vm/isolate.h	(working copy)
@@ -181,6 +181,14 @@
 
   Debugger* debugger() const { return debugger_; }
 
+  GcPrologueCallbacks& gc_prologue_callbacks() {
+    return gc_prologue_callbacks_;
+  }
+
+  GcEpilogueCallbacks& gc_epilogue_callbacks() {
+    return gc_epilogue_callbacks_;
+  }
+
   static void SetCreateCallback(Dart_IsolateCreateCallback cb) {
     create_callback_ = cb;
   }
@@ -202,14 +210,6 @@
     return shutdown_callback_;
   }
 
-  GcPrologueCallbacks& gc_prologue_callbacks() {
-    return gc_prologue_callbacks_;
-  }
-
-  GcEpilogueCallbacks& gc_epilogue_callbacks() {
-    return gc_epilogue_callbacks_;
-  }
-
  private:
   Isolate();