Store constant variable initializers in elements.

pkg/compiler/lib/src/dart_backend/backend.dart

Index: pkg/compiler/lib/src/dart_backend/backend.dart
diff --git a/pkg/compiler/lib/src/dart_backend/backend.dart b/pkg/compiler/lib/src/dart_backend/backend.dart
index 350118234dee958c63288bf142e2ff9adbd2307f..bec56aa7140863f50bbe80ca3174305c1ae018ed 100644
--- a/pkg/compiler/lib/src/dart_backend/backend.dart
+++ b/pkg/compiler/lib/src/dart_backend/backend.dart
@@ -473,11 +473,6 @@ class DartConstantTask extends ConstantCompilerTask
   }
 
   @override
-  ConstantExpression getConstantForVariable(VariableElement element) {
-    return constantCompiler.getConstantForVariable(element);
-  }
-
-  @override
   ConstantExpression getConstantForNode(Node node, TreeElements elements) {
     return constantCompiler.getConstantForNode(node, elements);
   }
@@ -507,9 +502,10 @@ class DartConstantTask extends ConstantCompilerTask
     });
   }
 
-  void compileVariable(VariableElement element) {
-    measure(() {
-      constantCompiler.compileVariable(element);
+  @override
+  ConstantExpression compileVariable(VariableElement element) {
+    return measure(() {
+      return constantCompiler.compileVariable(element);
     });
   }