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

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 <dlfcn.h>
+
+#include "include/dart_api.h"
+#include "platform/assert.h"
+#include "platform/globals.h"
+#include "bin/extensions.h"
+#include "bin/dartutils.h"
+
+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);
+}