Make ClassMirror.constructors an internal native and lazy.

runtime/vm/bootstrap_natives.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_BOOTSTRAP_NATIVES_H_
 #define VM_BOOTSTRAP_NATIVES_H_
 
 #include "vm/native_entry.h"
 
 // bootstrap dart natives used in the core dart library.
@@ skipping 233 matching lines @@
   V(Mirrors_makeLocalClassMirror, 1)                                           \
   V(Mirrors_makeLocalMirrorSystem, 0)                                          \
   V(InstanceMirror_invoke, 4)                                                  \
   V(InstanceMirror_invokeGetter, 3)                                            \
   V(InstanceMirror_invokeSetter, 4)                                            \
   V(ClosureMirror_apply, 2)                                                    \
   V(ClassMirror_name, 1)                                                       \
   V(ClassMirror_library, 1)                                                    \
   V(ClassMirror_supertype, 1)                                                  \
   V(ClassMirror_members, 2)                                                    \
+  V(ClassMirror_constructors, 2)                                               \
   V(LibraryMirror_members, 2)                                                  \
   V(ClassMirror_invoke, 4)                                                     \
   V(ClassMirror_invokeGetter, 3)                                               \
   V(ClassMirror_invokeSetter, 4)                                               \
   V(ClassMirror_invokeConstructor, 3)                                          \
   V(LibraryMirror_invoke, 4)                                                   \
   V(LibraryMirror_invokeGetter, 3)                                             \
   V(LibraryMirror_invokeSetter, 4)                                             \
   V(DeclarationMirror_metadata, 1)                                             \
   V(MethodMirror_name, 1)                                                      \
@@ skipping 22 matching lines @@
   static void DN_##name(Dart_NativeArguments args);
 
   BOOTSTRAP_NATIVE_LIST(DECLARE_BOOTSTRAP_NATIVE)
 
 #undef DECLARE_BOOTSTRAP_NATIVE
 };
 
 }  // namespace dart
 
 #endif  // VM_BOOTSTRAP_NATIVES_H_