Add native extensions for the Dart shell to mac and windows

runtime/bin/extensions_linux.cc

 // 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.
 
-#include <stdio.h>
+#include "bin/extensions.h"
 #include <dlfcn.h>
 
-#include "include/dart_api.h"
-#include "platform/assert.h"
-#include "platform/globals.h"
-#include "bin/extensions.h"
-#include "bin/dartutils.h"
+void* Extensions::LoadExtensionLibrary(const char* library_name) {
+  const char* strings[4] = { "./lib", library_name, ".so", NULL };
+  char* library_path = Concatenate(strings);
+  void* lib_handle = dlopen(library_path, RTLD_LAZY);
+  free(library_path);
+  return lib_handle;
+}
 
-Dart_Handle Extensions::LoadExtension(const char* extension_url,
-                                      Dart_Handle parent_library) {
-  // TODO(whesse): Consider making loading extensions lazy, so the
-  // dynamic library is loaded only when first native function is called.
-  ASSERT(DartUtils::IsDartExtensionSchemeURL(extension_url));
-  const char* library_name =
-      extension_url + strlen(DartUtils::kDartExtensionScheme);
-  if (strchr(library_name, '/') != NULL) {
-    return Dart_Error("path components not allowed in extension library name");
-  }
-  const int buffer_length = strlen(library_name) + strlen("./lib.so") + 1;
-  char* library_path = new char[buffer_length];
-  snprintf(library_path, buffer_length, "./lib%s.so", library_name);
-
-  void* lib_handle = dlopen(library_path, RTLD_LAZY);
-  if (!lib_handle) {
-    delete[] library_path;
-    return Dart_Error("cannot find extension library");
-  }
-  // Reuse library_path buffer for intialization function name.
-  char* library_init_function = library_path;
-  snprintf(library_init_function, buffer_length, "%s_Init", library_name);
-  typedef Dart_Handle (*InitFunctionType)(Dart_Handle import_map);
-  InitFunctionType fn = reinterpret_cast<InitFunctionType>(
-      dlsym(lib_handle, library_init_function));
-  delete[] library_path;
-  char *error = dlerror();
-  if (error != NULL) {
-    return Dart_Error(error);
-  }
-  return (*fn)(parent_library);
+void* Extensions::ResolveSymbol(void* lib_handle, const char* symbol) {
+  void* result = dlsym(lib_handle, symbol);
+  if (dlerror() != NULL) return NULL;
+  return result;
 }