Add ConstantConstructor to ConstantExpression system.

pkg/compiler/lib/src/elements/elements.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library elements;
 
 
 import '../constants/expressions.dart';
 import '../tree/tree.dart';
 import '../util/util.dart';
@@ skipping 980 matching lines @@
   Name get memberName;
 }
 
 /// A function, variable or parameter defined in an executable context.
 abstract class LocalElement extends Element implements TypedElement, Local {
 }
 
 /// A top level, static or instance field, a formal parameter or local variable.
 abstract class VariableElement extends ExecutableElement {
   Expression get initializer;
+
+  /// The constant expression defining the value of the variable if `const`,
+  /// `null` otherwise.
+  ConstantExpression get constant;
 }
 
 /// An entity that defines a local entity (memory slot) in generated code.
 ///
 /// Parameters, local variables and local functions (can) define local entity
 /// and thus implement [Local] through [LocalElement]. For non-element locals,
 /// like `this` and boxes, specialized [Local] classes are created.
 ///
 /// Type variables can introduce locals in factories and constructors
 /// but since one type variable can introduce different locals in different
@@ skipping 238 matching lines @@
   /// Consider for instance this hierarchy:
   ///
   ///     class C { C.c(a, {b});
   ///     class D {}
   ///     class E = C with D;
   ///
   /// Class `E` has a synthesized constructor, `E.c`, whose defining constructor
   /// is `C.c`.
   ConstructorElement get definingConstructor;
 
+  /// The constant constructor defining the binding of fields if `const`,
+  /// `null` otherwise.
+  ConstantConstructor get constantConstructor;
+
+  /// `true` if this constructor is either `bool.fromEnviroment`
+  bool get isFromEnvironmentConstructor;
+
   /// Use [enclosingClass] instead.
   @deprecated
   get enclosingElement;
 }
 
 /// JavaScript backend specific element for the body of constructor.
 // TODO(johnniwinther): Remove this class from the element model.
 abstract class ConstructorBodyElement extends MethodElement {
   FunctionElement get constructor;
 }
@@ skipping 363 matching lines @@
   bool get isDeclaredByField;
 
   /// Returns `true` if this member is abstract.
   bool get isAbstract;
 
   /// If abstract, [implementation] points to the overridden concrete member,
   /// if any. Otherwise [implementation] points to the member itself.
   Member get implementation;
 }