Add native extensions to the Dart shell, on the linux platform.

runtime/bin/test_extension_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 <string.h>
+
+#include "../include/dart_api.h"
+
+#define EXPORT_SYMBOL __attribute__ ((visibility ("default")))
+
+extern "C" Dart_NativeFunction ResolveName(Dart_Handle name, int argc);
+
+extern "C" EXPORT_SYMBOL Dart_Handle test_extension_Init(Dart_Handle library) {
+  if (Dart_IsError(library)) return library;
+  Dart_Handle check_return = Dart_SetNativeResolver(library, ResolveName);
+  if (Dart_IsError(check_return)) return check_return;
+  return Dart_Null();
+}
+
+extern "C" void IfNull(Dart_NativeArguments arguments) {
+  Dart_Handle object = Dart_GetNativeArgument(arguments, 0);
+  if (Dart_IsNull(object)) {
+    Dart_SetReturnValue(arguments, Dart_GetNativeArgument(arguments, 1));
+  } else {
+    Dart_SetReturnValue(arguments, object);
+  }
+}
+
+extern "C" Dart_NativeFunction ResolveName(Dart_Handle name, int argc) {
+  assert(Dart_IsString8(name));
+  const char* cname;
+  Dart_Handle check_error;
+
+  check_error = Dart_StringToCString(name, &cname);
+  if (Dart_IsError(check_error)) return NULL;
+  if (!strcmp("Cat_IfNull", cname) && argc == 2) {
+    return IfNull;
+  }
+  return NULL;
+}