fixes #173, ability to use native JS indexers

lib/src/utils.dart

Index: lib/src/utils.dart
diff --git a/lib/src/utils.dart b/lib/src/utils.dart
index 4c7339520c673f724b77c967c1d74164a4615bbe..d89e05ac18e48ee26b658c12761ebe32aae836b8 100644
--- a/lib/src/utils.dart
+++ b/lib/src/utils.dart
@@ -349,7 +349,7 @@ String resourceOutputPath(Uri resourceUri, Uri entryUri) {
 ///
 ///    (v) => v.type.name == 'Deprecated' && v.type.element.library.isDartCore
 ///
-DartObjectImpl getAnnotationValue(
+DartObjectImpl findNodeAnnotation(
     AnnotatedNode node, bool test(DartObjectImpl value)) {

[vsm, 2015/05/20 19:15:29]

Could this just call findElementAnnotation(node.element)?

[Jennifer Messerly, 2015/05/20 19:25:32]

you'd think so, but AnnotatedNode doesn't have .element.
Of its three subtypes, Declaration and Directive both have a .element. However
VariableDeclarationList does not. I guess because of cases like:

    @deprecated
    var foo, bar, baz;

yet more reasons VariableDeclarationList is the most annoying thing ever :)
anyway, it does look like we could convert existing usage over to
findElementAnnotation, and just `.element` on the outside. does that work for
you?

[vsm, 2015/05/20 19:39:50]

sgtm

   for (var metadata in node.metadata) {
     ElementAnnotationImpl element = metadata.elementAnnotation;
@@ -364,6 +364,19 @@ DartObjectImpl getAnnotationValue(
   return null;
 }
 
+/// Similar to [findNodeAnnotation] but starts from any element.
+DartObjectImpl findElementAnnotation(
+    Element element, bool test(DartObjectImpl value)) {
+  for (var metadata in element.metadata) {
+    var evalResult = metadata.evaluationResult;
+    if (evalResult == null) continue;
+
+    var value = evalResult.value;
+    if (value != null && test(value)) return value;
+  }
+  return null;
+}
+
 /// Given a constant [value], a [fieldName], and an [expectedType], returns the
 /// value of that field.
 ///