Support snapshots in sky_shell (again)

sky/tools/packager/loader.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sky/tools/packager/loader.h"
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/logging.h"
@@ skipping 75 matching lines @@
   Dart_Handle result = Dart_LoadSource(library, url, source, 0, 0);
   LogIfError(result);
   return result;
 }
 
 Loader* g_loader = nullptr;
 
 Loader& GetLoader() {
   if (!g_loader) {
     base::CommandLine& command_line = *base::CommandLine::ForCurrentProcess();
-    CHECK(command_line.HasSwitch(kPackageRoot)) << "Need --package-root";
-    g_loader = new Loader(command_line.GetSwitchValuePath(kPackageRoot));
+    CHECK(command_line.HasSwitch(switches::kPackageRoot))
+        << "Need --package-root";
+    g_loader =
+        new Loader(command_line.GetSwitchValuePath(switches::kPackageRoot));
   }
   return *g_loader;
 }
 
 }  // namespace
 
 Dart_Handle HandleLibraryTag(Dart_LibraryTag tag,
                              Dart_Handle library,
                              Dart_Handle url) {
   CHECK(Dart_IsLibrary(library));
   CHECK(Dart_IsString(url));
 
   if (tag == Dart_kCanonicalizeUrl)
     return GetLoader().CanonicalizeURL(library, url);
 
   if (tag == Dart_kImportTag)
     return GetLoader().Import(url);
 
   if (tag == Dart_kSourceTag)
     return GetLoader().Source(library, url);
 
   return Dart_NewApiError("Unknown library tag.");
 }
 
 void LoadScript(const std::string& url) {
   LogIfError(
       Dart_LoadScript(StringToDart(url), StringToDart(Fetch(url)), 0, 0));
 }