Migrate DDC to the new analysis driver.

pkg/dev_compiler/lib/src/compiler/element_helpers.dart

Index: pkg/dev_compiler/lib/src/compiler/element_helpers.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/element_helpers.dart b/pkg/dev_compiler/lib/src/compiler/element_helpers.dart
index 0937565ae7f1e3691c226841728ddc61351abde6..522532d4d3a55391d586e30405cb25946ff53d10 100644
--- a/pkg/dev_compiler/lib/src/compiler/element_helpers.dart
+++ b/pkg/dev_compiler/lib/src/compiler/element_helpers.dart
@@ -58,7 +58,7 @@ class Tuple2<T0, T1> {
 ///
 DartObject findAnnotation(Element element, bool test(DartObjectImpl value)) {
   for (var metadata in element.metadata) {
-    var value = metadata.computeConstantValue();
+    var value = metadata.constantValue;
     if (value != null && test(value)) return value;
   }
   return null;