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

sky/engine/core/script/dart_loader.cc

Index: sky/engine/core/script/dart_loader.cc
diff --git a/sky/engine/core/script/dart_loader.cc b/sky/engine/core/script/dart_loader.cc
index 62a72ea0bcce5fdf92917fc7e631448db01ced12..19a878e44941e92ef93dd6fbe098b0b4fb5924db 100644
--- a/sky/engine/core/script/dart_loader.cc
+++ b/sky/engine/core/script/dart_loader.cc
@@ -26,11 +26,12 @@ Dart_Handle CanonicalizeURL(DartState* state,
                             Dart_Handle library,
                             Dart_Handle url) {
   String string = StringFromDart(url);
+  String original = string;

[abarth-chromium, 2015/03/13 20:38:02]

Remove?

   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);