feat(dart/transform): Add a di transformer

Add a transformer for `di` which generates `.ng_deps.dart` files for all
`.dart` files it is run on. These `.ng_deps.dart` files register
metadata for any `@Injectable` classes.

Fix unit tests for changes introduced by the di transformer.

When using `pub (build|serve) --mode=ngstatic`, we will also generate
getters and setters, parse templates, and remove import of `dart:mirrors`
in the Angular transform. Because this is still relatively immature, we
use the mode to keep it opt-in for now.

Closes #700

modules/angular2/src/transform/reflection_remover/rewriter.dart

@@ -81,7 +81,7 @@ class Rewriter {
 
   String _commentedNode(AstNode node) {
     // TODO(kegluneq): Return commented code once we generate all needed code.
-    return _code.substring(node.offset, node.end);
+    return '/*${_code.substring(node.offset, node.end)}*/';
   }
 }