Cleanup in //runtime/bin

runtime/bin/extensions.h

Index: runtime/bin/extensions.h
diff --git a/runtime/bin/extensions.h b/runtime/bin/extensions.h
index 8c172b85ff89cb840f00dff4c4b766ce941dd1bd..da18615ba7537b9e131266ed3dabb902d914f5f9 100644
--- a/runtime/bin/extensions.h
+++ b/runtime/bin/extensions.h
@@ -8,7 +8,6 @@
 #include "include/dart_api.h"
 #include "platform/globals.h"
 
-
 namespace dart {
 namespace bin {
 
@@ -28,8 +27,8 @@ class Extensions {
  private:
   static Dart_Handle GetError();
 
-  // The returned string must be freed.
-  static char* Concatenate(const char** strings);
+  // The returned string is scope allocated.
+  static const char* Concatenate(const char** strings);
 
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Extensions);