Minor restructure some of the builtin library processing code

bin/builtin.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 BIN_BUILTIN_H_
 #define BIN_BUILTIN_H_
 
 #include <stdio.h>
 #include <stdlib.h>
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/globals.h"
 
 #define FUNCTION_NAME(name) Builtin_##name
 #define REGISTER_FUNCTION(name, count)                                         \
   { ""#name, FUNCTION_NAME(name), count },
 #define DECLARE_FUNCTION(name, count)                                          \
   extern void FUNCTION_NAME(name)(Dart_NativeArguments args);
 
 
 class Builtin {
  public:
   enum BuiltinLibraryId {
-    kBuiltinLibrary,
+    // These libraries are included in the core snapshot.
+    kBuiltinLibrary = 0,
+    kJsonLibrary,
+    kUriLibrary,
+
+    // These libraries are not included in the core snapshot.
     kCryptoLibrary,
     kIOLibrary,
-    kJsonLibrary,
-    kUriLibrary,
     kUtfLibrary,
+
+    kInvalidLibrary,
   };
 
   static Dart_Handle Source(BuiltinLibraryId id);
   static void SetupLibrary(Dart_Handle library, BuiltinLibraryId id);
   static Dart_Handle LoadLibrary(BuiltinLibraryId id);
   static void ImportLibrary(Dart_Handle library, BuiltinLibraryId id);
   static void SetNativeResolver(BuiltinLibraryId id);
   static void PrintString(FILE* out, Dart_Handle object);
 
  private:
   static Dart_NativeFunction NativeLookup(Dart_Handle name,
                                           int argument_count);
 
   static const char builtin_source_[];
   static const char crypto_source_[];
   static const char io_source_[];
   static const char json_source_[];
   static const char uri_source_[];
   static const char utf_source_[];
 
+  typedef struct {
+    const char* url_;
+    const char* source_;
+    bool has_natives_;
+  } builtin_lib_props;
+  static builtin_lib_props builtin_libraries_[];
+
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Builtin);
 };
 
 
 #endif  // BIN_BUILTIN_H_