Reapply (plus add some more) Entity-ify some portions of LocalsHandler and Closure.

pkg/compiler/lib/src/closure.dart

Index: pkg/compiler/lib/src/closure.dart
diff --git a/pkg/compiler/lib/src/closure.dart b/pkg/compiler/lib/src/closure.dart
index 6dacea63154b7b81b3c29e4ce148533d4e327ae1..50d827a2591f2d66ab902ce7b82d1d2653ecf4fa 100644
--- a/pkg/compiler/lib/src/closure.dart
+++ b/pkg/compiler/lib/src/closure.dart
@@ -130,15 +130,10 @@ class ClosureTask extends CompilerTask implements ClosureClassMaps {
   }
 }
 
-/// Common interface for [BoxFieldElement] and [ClosureFieldElement] as
-/// non-elements.
-// TODO(johnniwinther): Remove `implements Element`.
-abstract class CapturedVariable implements Element {}
-
 // TODO(ahe): These classes continuously cause problems.  We need to
 // find a more general solution.
 class ClosureFieldElement extends ElementX
-    implements FieldElement, CapturedVariable, PrivatelyNamedJSEntity {
+    implements FieldElement, PrivatelyNamedJSEntity {
   /// The [BoxLocal] or [LocalElement] being accessed through the field.
   final Local local;
 
@@ -295,11 +290,7 @@ class BoxLocal extends Local {
 // TODO(ngeoffray, ahe): These classes continuously cause problems.  We need to
 // find a more general solution.
 class BoxFieldElement extends ElementX
-    implements
-        TypedElement,
-        CapturedVariable,
-        FieldElement,
-        PrivatelyNamedJSEntity {
+    implements TypedElement, FieldElement, PrivatelyNamedJSEntity {
   final BoxLocal box;
 
   BoxFieldElement(String name, this.variableElement, BoxLocal box)
@@ -422,7 +413,7 @@ class ClosureScope {
   // If the scope is attached to a [For] contains the variables that are
   // declared in the initializer of the [For] and that need to be boxed.
   // Otherwise contains the empty List.
-  List<VariableElement> boxedLoopVariables = const <VariableElement>[];
+  List<Local> boxedLoopVariables = const <Local>[];
 
   ClosureScope(this.boxElement, this.capturedVariables);
 
@@ -482,8 +473,7 @@ class ClosureClassMap {
 
   /// Maps free locals, arguments, function elements, and box locals to
   /// their locations.
-  final Map<Local, CapturedVariable> freeVariableMap =
-      new Map<Local, CapturedVariable>();
+  final Map<Local, FieldEntity> freeVariableMap = new Map<Local, FieldEntity>();
 
   /// Maps [Loop] and [FunctionExpression] nodes to their [ClosureScope] which
   /// contains their box and the captured variables that are stored in the box.
@@ -513,7 +503,7 @@ class ClosureClassMap {
     return freeVariableMap.containsKey(element);
   }
 
-  void forEachFreeVariable(f(Local variable, CapturedVariable field)) {
+  void forEachFreeVariable(f(Local variable, FieldEntity field)) {
     freeVariableMap.forEach(f);
   }
 
@@ -530,14 +520,14 @@ class ClosureClassMap {
   }
 
   bool isVariableBoxed(Local variable) {
-    CapturedVariable copy = freeVariableMap[variable];
+    FieldEntity copy = freeVariableMap[variable];
     if (copy is BoxFieldElement) {
       return true;
     }
     return capturingScopesBox(variable);
   }
 
-  void forEachCapturedVariable(void f(Local variable, CapturedVariable field)) {
+  void forEachCapturedVariable(void f(Local variable, FieldEntity field)) {
     freeVariableMap.forEach((variable, copy) {
       if (variable is BoxLocal) return;
       f(variable, copy);