Implement correct scoping rules for variables.

sdk/lib/_internal/compiler/implementation/resolution/scope.dart

Index: sdk/lib/_internal/compiler/implementation/resolution/scope.dart
diff --git a/sdk/lib/_internal/compiler/implementation/resolution/scope.dart b/sdk/lib/_internal/compiler/implementation/resolution/scope.dart
index 81eadaebbfd52814cf78aa4811fd73e8ee023b46..323d9523c9c8295d2d7199caa4a10da9303aa8f3 100644
--- a/sdk/lib/_internal/compiler/implementation/resolution/scope.dart
+++ b/sdk/lib/_internal/compiler/implementation/resolution/scope.dart
@@ -41,24 +41,6 @@ abstract class NestedScope extends Scope {
   }
 }
 
-class VariableDefinitionScope extends NestedScope {
-  final SourceString variableName;
-  bool variableReferencedInInitializer = false;
-
-  VariableDefinitionScope(Scope parent, this.variableName) : super(parent);
-
-  Element localLookup(SourceString name) {
-    if (name == variableName) {
-      variableReferencedInInitializer = true;
-    }
-    return null;
-  }
-
-  Element add(Element newElement) {
-    throw "Cannot add element to VariableDefinitionScope";
-  }
-}
-
 /**
  * [TypeDeclarationScope] defines the outer scope of a type declaration in
  * which the declared type variables and the entities in the enclosing scope are
@@ -75,7 +57,7 @@ class TypeDeclarationScope extends NestedScope {
   }
 
   Element add(Element newElement) {
-    throw "Cannot add element to TypeDeclarationScope";
+    throw "Cannot add element to TypeDeclarationScope($element)";
   }
 
   Element lookupTypeVariable(SourceString name) {
@@ -96,41 +78,33 @@ class TypeDeclarationScope extends NestedScope {
       'TypeDeclarationScope($element)';
 }
 
-abstract class MutableScope extends NestedScope {
+class BlockScope extends NestedScope {
   final Map<SourceString, Element> elements;
 
-  MutableScope(Scope parent)
-      : super(parent),
-        this.elements = new Map<SourceString, Element>() {
+  BlockScope(Scope parent)
+      : elements = <SourceString, Element>{}, super(parent) {
     assert(parent != null);
   }
 
-  Element add(Element newElement) {
-    if (elements.containsKey(newElement.name)) {
-      return elements[newElement.name];
-    }
-    elements[newElement.name] = newElement;
-    return newElement;
+  Element add(Element element) {
+    return elements.putIfAbsent(element.name, () => element);
   }
 
   Element localLookup(SourceString name) => elements[name];
+
+  String toString() => 'BlockScope(${elements.keys.toList()})';
 }
 
-class MethodScope extends MutableScope {
+class MethodScope extends BlockScope {
   final Element element;
 
-  MethodScope(Scope parent, this.element)
-      : super(parent);
+  MethodScope(Scope parent, this.element) : super(parent) {
+    assert(elements != null);
+  }
 
   String toString() => 'MethodScope($element${elements.keys.toList()})';
 }
 
-class BlockScope extends MutableScope {
-  BlockScope(Scope parent) : super(parent);
-
-  String toString() => 'BlockScope(${elements.keys.toList()})';
-}
-
 /**
  * [ClassScope] defines the inner scope of a class/interface declaration in
  * which declared members, declared type variables, entities in the enclosing