Handle const loop variable.

pkg/compiler/lib/src/resolution/members.dart

Index: pkg/compiler/lib/src/resolution/members.dart
diff --git a/pkg/compiler/lib/src/resolution/members.dart b/pkg/compiler/lib/src/resolution/members.dart
index c41d5a1517f135e38515b03ed4cf5b3bc0ec6af4..460b34ef6da702008b527bc72c89685b85f82ab9 100644
--- a/pkg/compiler/lib/src/resolution/members.dart
+++ b/pkg/compiler/lib/src/resolution/members.dart
@@ -126,7 +126,7 @@ class ResolverVisitor extends MappingVisitor<ResolutionResult> {
   /// When visiting the type declaration of the variable in a [ForIn] loop,
   /// the initializer of the variable is implicit and we should not emit an
   /// error when verifying that all final variables are initialized.
-  bool allowFinalWithoutInitializer = false;
+  bool inLoopVariable = false;
 
   /// The nodes for which variable access and mutation must be registered in
   /// order to determine when the static type of variables types is promoted.
@@ -4387,10 +4387,10 @@ class ResolverVisitor extends MappingVisitor<ResolutionResult> {
       Scope blockScope) {
     LibraryElement library = enclosingElement.library;
 
-    bool oldAllowFinalWithoutInitializer = allowFinalWithoutInitializer;
-    allowFinalWithoutInitializer = true;
+    bool oldAllowFinalWithoutInitializer = inLoopVariable;
+    inLoopVariable = true;
     visitIn(declaration, blockScope);
-    allowFinalWithoutInitializer = oldAllowFinalWithoutInitializer;
+    inLoopVariable = oldAllowFinalWithoutInitializer;
 
     Send send = declaration.asSend();
     VariableDefinitions variableDefinitions =