Added for-loop variable tracking and regular closures/initializers captured variable tracking.

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 44fcc597ac039edf58f5376b60500ac5a9568348..bd7a1a6205a6b658c9fdbcd22c62b1467c0159cc 100644
--- a/pkg/compiler/lib/src/closure.dart
+++ b/pkg/compiler/lib/src/closure.dart
@@ -100,9 +100,6 @@ class ScopeInfo {
 
   /// True if [variable] has been mutated and is also used in another scope.
   bool isBoxed(Local variable) => false;
-
-  /// True if this scope declares any variables that need to be boxed.
-  bool get hasBoxedVariables => false;
 }
 
 /// Class representing the usage of a scope that has been captured in the
@@ -141,6 +138,27 @@ class ClosureScope extends ScopeInfo {
 /// each iteration, by boxing the iteration variable[s].
 class LoopClosureScope extends ClosureScope {
   const LoopClosureScope();
+
+  /// True if this loop scope declares in the first part of the loop
+  /// `for (<here>;...;...)` any variables that need to be boxed.
+  bool get hasBoxedLoopVariables => false;
+
+  /// The set of iteration variables (or variables declared in the for loop
+  /// expression (`for (<here>; ... ; ...)`) that need to be boxed to snapshot
+  /// their value. These variables are also included in the set of
+  /// `forEachBoxedVariable` method. The distinction between these two sets is
+  /// in this example:
+  ///
+  ///     run(f) => f();
+  ///     var a;
+  ///     for (int i = 0; i < 3; i++) {
+  ///       var b = 3;
+  ///       a = () => b = i;
+  ///     }
+  ///
+  /// `i` would be a part of the boxedLoopVariables AND boxedVariables, but b
+  /// would only be a part of boxedVariables.
+  List<Local> get boxedLoopVariables => const <Local>[];
 }
 
 /// Class that describes the actual mechanics of how the converted, rewritten
@@ -647,18 +665,10 @@ class ClosureScopeImpl implements ClosureScope, LoopClosureScope {
   bool get requiresContextBox => capturedVariables.keys.isNotEmpty;
 
   void forEachBoxedVariable(f(Local local, FieldEntity field)) {
-    if (capturedVariables.isNotEmpty) {
-      capturedVariables.forEach(f);
-    } else {
-      for (Local l in boxedLoopVariables) {
-        // The boxes for loop variables are constructed on-demand per-iteration
-        // in the locals handler.
-        f(l, null);
-      }
-    }
+    capturedVariables.forEach(f);
   }
 
-  bool get hasBoxedVariables => !capturedVariables.isEmpty;
+  bool get hasBoxedLoopVariables => boxedLoopVariables.isNotEmpty;
 
   bool isBoxed(Local variable) {
     return capturedVariables.containsKey(variable);
@@ -746,9 +756,6 @@ class ClosureClassMap implements ClosureRepresentationInfo {
   ClosureClassMap(this.closureEntity, this.closureClassEntity, this.callMethod,
       this.thisLocal);
 
-  bool get hasBoxedVariables =>
-      throw new UnsupportedError("ClosureClassMap.hasBoxedVariables");
-
   List<Local> get createdFieldEntities {
     List<Local> fields = <Local>[];
     if (closureClassEntity == null) return const <Local>[];