Add native extensions for the Dart shell to mac and windows

runtime/bin/extensions.cc

Index: runtime/bin/extensions.cc
diff --git a/runtime/bin/extensions.cc b/runtime/bin/extensions.cc
new file mode 100644
index 0000000000000000000000000000000000000000..afcb29fdc52a10ba9222e1c0c63e68becdcad562
--- /dev/null
+++ b/runtime/bin/extensions.cc
@@ -0,0 +1,57 @@
+// 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 "bin/extensions.h"
+
+#include <stdio.h>
+
+#include "include/dart_api.h"
+#include "platform/assert.h"
+#include "platform/globals.h"
+#include "bin/dartutils.h"
+
+Dart_Handle Extensions::LoadExtension(const char* extension_url,
+                                      Dart_Handle parent_library) {
+  ASSERT(DartUtils::IsDartExtensionSchemeURL(extension_url));
+  const char* library_name =
+      extension_url + strlen(DartUtils::kDartExtensionScheme);
+  if (strchr(library_name, '/') != NULL ||
+      strchr(library_name, '\\') != NULL) {
+    return Dart_Error("path components not allowed in extension library name");
+  }
+  void* library_handle = LoadExtensionLibrary(library_name);
+  if (!library_handle) {
+    return Dart_Error("cannot find extension library");
+  }
+
+  const char* strings[3] = { library_name, "_Init", NULL };
+  char* init_function_name = Concatenate(strings);
+  typedef Dart_Handle (*InitFunctionType)(Dart_Handle import_map);
+  InitFunctionType fn = reinterpret_cast<InitFunctionType>(
+      ResolveSymbol(library_handle, init_function_name));
+  free(init_function_name);
+
+  if (fn == NULL) {
+    return Dart_Error("cannot find initialization function in extension");
+  }
+  return (*fn)(parent_library);
+}
+
+
+// Concatenates a NULL terminated array of strings.
+// The returned string must be freed.
+char* Extensions::Concatenate(const char** strings) {
+  int size = 1;  // null termination.
+  for (int i = 0; strings[i] != NULL; i++) {
+    size += strlen(strings[i]);
+  }
+  char* result = reinterpret_cast<char*>(malloc(size));
+  int index = 0;
+  for (int i = 0; strings[i] != NULL; i++) {
+    index += snprintf(result + index, size - index, "%s", strings[i]);
+  }
+  ASSERT(index == size - 1);
+  ASSERT(result[size - 1] == '\0');
+  return result;
+}