Add native extensions for the Dart shell to mac and windows

runtime/bin/extensions.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_EXTENSIONS_H_
 #define BIN_EXTENSIONS_H_
 
 #include "include/dart_api.h"
 #include "platform/globals.h"
 
 class Extensions {
  public:
-  // TODO(whesse): Make loading extensions lazy, so dynamic library is loaded
-  // only when first native function is called.
   // TODO(whesse): Make extension load from a relative path relative to
   // the library it is in.  Currently loads from current working directory.
   static Dart_Handle LoadExtension(const char* extension_url,
                                    Dart_Handle library);

[Ivan Posva, 2012/03/07 19:06:23]

library -> parent_library
Without any documentation it is entirely unclear what library you expect here.
The .cc file actually uses parent_library.

[Bill Hesse, 2012/03/08 12:04:37]

Done.

+  static char* MakeString(const char* format, const char* name);

[Mads Ager (google), 2012/03/07 14:31:48]

This one should not be exposed in the Extensions class. It is very specific
about the format. I would either make it a static helper method in the
implementation file or just inline the code.

[Bill Hesse, 2012/03/08 12:04:37]

It is used in both the platform-specific and platform-independent files, so it
cannot be a static helper method (unless it is in the header file).  It really
cleans up the implementation to have this - otherwise, we are tempted to share
the same buffer for both things, and need to pass it into the platform-specific
functions.

It should be private, though.

+
+  // Platform-specific implementations.
+  static void* LoadExtensionLibrary(const char* library_name);

[Mads Ager (google), 2012/03/07 14:31:48]

Could these two be private?

[Bill Hesse, 2012/03/08 12:04:37]

Yes.

+  static void* ResolveSymbol(void* lib_handle, const char* symbol);
+
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Extensions);
 };
 
 #endif  // BIN_EXTENSIONS_H_