Add fields to platform library, implement them on runtime dart.

runtime/bin/dartutils.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_DARTUTILS_H_
 #define BIN_DARTUTILS_H_
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 
@@ skipping 186 matching lines @@
   static const char* original_working_directory;
 
   static const char* kDartScheme;
   static const char* kDartExtensionScheme;
   static const char* kAsyncLibURL;
   static const char* kBuiltinLibURL;
   static const char* kCoreLibURL;
   static const char* kIOLibURL;
   static const char* kIOLibPatchURL;
   static const char* kUriLibURL;
+  static const char* kPlatformLibURL;
   static const char* kHttpScheme;
 
   static const char* kIdFieldName;
 
   static uint8_t magic_number[];
 
  private:
   static const char* GetCanonicalPath(const char* reference_dir,
                                       const char* filename);
 
@@ skipping 302 matching lines @@
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CObjectExternalUint8Array);
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_DARTUTILS_H_