Port the remaining of dart:core to the unified corelib.

lib/compiler/implementation/elements/elements.dart

Index: lib/compiler/implementation/elements/elements.dart
diff --git a/lib/compiler/implementation/elements/elements.dart b/lib/compiler/implementation/elements/elements.dart
index 1d951796313ebf2a8e5288d1ba8c9784d315d79c..c98ab47d9817488da00722f8f6932903eff37b52 100644
--- a/lib/compiler/implementation/elements/elements.dart
+++ b/lib/compiler/implementation/elements/elements.dart
@@ -444,7 +444,16 @@ class VariableElement extends Element {
                   ElementKind kind,
                   Element enclosing,
                   [Node node])
-    : super(name, kind, enclosing), cachedNode = node;
+      : super(name, kind, enclosing), cachedNode = node;
+
+  VariableElement.from(SourceString name,
+                       VariableElement other,
+                       Element enclosing)
+      : this(name,
+             new VariableListElement.from(other.variables, enclosing),
+             other.kind,
+             enclosing,
+             other.cachedNode);
 
   Node parseNode(DiagnosticListener listener) {
     if (cachedNode !== null) return cachedNode;
@@ -522,6 +531,24 @@ class VariableListElement extends Element {
       this.cachedNode = node,
       this.modifiers = node.modifiers;
 
+  factory VariableListElement.from(VariableListElement other,
+                                   Element enclosing) {
+    var variableList;
+    if (other is PartialFieldListElement) {
+      variableList = new PartialFieldListElement(other.beginToken,
+                                                 other.endToken,
+                                                 other.modifiers,
+                                                 enclosing);
+    } else {
+      variableList = new VariableListElement(other.kind,
+                                             other.modifiers,
+                                             enclosing);
+    }
+    variableList.cachedNode = other.cachedNode;
+    variableList.type = other.type;
+    return variableList;
+  }
+
   VariableDefinitions parseNode(DiagnosticListener listener) {
     return cachedNode;
   }