Make package: work like Dart expects in preparation for a Sky SDK

sky/engine/core/script/dart_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/engine/config.h"
 #include "sky/engine/core/script/dart_loader.h"
 
 #include "base/callback.h"
 #include "mojo/common/data_pipe_drainer.h"
 #include "sky/engine/core/script/dart_dependency_catcher.h"
@@ skipping 12 matching lines @@
 namespace {
 
 Dart_Handle CanonicalizeURL(DartState* state,
                             Dart_Handle library,
                             Dart_Handle url) {
   String string = StringFromDart(url);
   if (string.startsWith("dart:") || string.startsWith("mojo:"))
     return url;
   // TODO(dart): Figure out how 'package:' should work in sky.
   if (string.startsWith("package:")) {
-    string.replace("package:", "/gen/");
+    string.replace("package:", "/packages/");
   }
   String library_url_string = StringFromDart(Dart_LibraryUrl(library));
   KURL library_url = KURL(ParsedURLString, library_url_string);
   KURL resolved_url = KURL(library_url, string);
   return StringToDart(state, resolved_url.string());
 }
 
 }  // namespace
 
 // A DartLoader::Job represents a network load. It fetches data from the network
@@ skipping 239 matching lines @@
 
   WatcherSignaler watcher_signaler(*this, job);
 
   LOG(ERROR) << "Library Load failed: " << job->url().string().utf8().data();
   // TODO(eseidel): Call Dart_LibraryHandleError in the SourceJob case?
 
   jobs_.remove(job);
 }
 
 }  // namespace blink