Starting making dart2js strong mode clean.

pkg/compiler/lib/src/js_backend/namer.dart

Index: pkg/compiler/lib/src/js_backend/namer.dart
diff --git a/pkg/compiler/lib/src/js_backend/namer.dart b/pkg/compiler/lib/src/js_backend/namer.dart
index 3f284c490b1a01eb45c605e9a031656c82ff48f9..15751cfe3a2151b13cfdc64b33968b6d889e757c 100644
--- a/pkg/compiler/lib/src/js_backend/namer.dart
+++ b/pkg/compiler/lib/src/js_backend/namer.dart
@@ -1924,7 +1924,7 @@ class ConstantNamingVisitor implements ConstantValueVisitor {
 
     // TODO(johnniwinther): This should be accessed from a codegen closed world.
     codegenWorldBuilder.forEachInstanceField(constant.type.element,
-        (_, FieldElement field) {
+        (_, FieldEntity field) {
       if (failed) return;
       _visit(constant.fields[field]);
     });
@@ -2051,7 +2051,7 @@ class ConstantCanonicalHasher implements ConstantValueVisitor<int, Null> {
   int visitConstructed(ConstructedConstantValue constant, [_]) {
     int hash = _hashString(3, constant.type.element.name);
     codegenWorldBuilder.forEachInstanceField(constant.type.element,
-        (_, FieldElement field) {
+        (_, FieldEntity field) {
       hash = _combine(hash, _visit(constant.fields[field]));
     });
     return hash;