Teach dart_package to understand the packages/ subdirectory

build/module_args/mojo.gni

Index: build/module_args/mojo.gni
diff --git a/build/module_args/mojo.gni b/build/module_args/mojo.gni
index d7cf153c60816b2416198d1395f94fda15462ec7..94deea0bc1fefd0b2f689d60daffe3bef72f58f1 100644
--- a/build/module_args/mojo.gni
+++ b/build/module_args/mojo.gni
@@ -5,6 +5,10 @@
 # This variable should point to the parent directory of the Mojo SDK.
 mojo_sdk_root = "//"
 
+# This variable should point to the parent directory of the Dart SDK. It can be

[tonyg, 2015/04/08 13:52:37]

It's not really clear to me why this should point to the parent instead of
"//third_party/dart-sdk/dart-sdk/"

[blundell, 2015/04/09 11:53:41]

Just for consistency with mojo_sdk_root :).

+# omitted if Dart is not being used.
+mojo_dart_sdk_root = "//third_party/dart-sdk/"
+
 # To build the Mojo shell from source, set this variable to true. To use the
 # prebuilt shell, omit this variable or set it to false. Note that the prebuilt
 # shell will be used only on platforms for which it is published (currently