Add an SDK source.

lib/src/flutter.dart

Index: lib/src/flutter.dart
diff --git a/lib/src/flutter.dart b/lib/src/flutter.dart
index cb383e460db5191b1aa0ef8d2ae58938d27b9de1..cf6c0d45030271f1bff5fa752236c4cd54dce129 100644
--- a/lib/src/flutter.dart
+++ b/lib/src/flutter.dart
@@ -23,3 +23,10 @@ final version = () {
   return new Version.parse(
       readTextFile(p.join(rootDirectory, "version")).trim());
 }();
+
+/// Returns the path to the package [name] within Flutter.
+String packagePath(String name) {
+  if (!isAvailable) throw new StateError("Flutter is not available.");
+
+  return p.join(rootDirectory, 'packages', name);
+}