Refactor ConstantExpression/ConstantConstructor to use entities.

pkg/compiler/lib/src/constants/constant_constructors.dart

Index: pkg/compiler/lib/src/constants/constant_constructors.dart
diff --git a/pkg/compiler/lib/src/constants/constant_constructors.dart b/pkg/compiler/lib/src/constants/constant_constructors.dart
index 7572883a4028d683f5dd292bbe64623fa9a9a8df..3ffae34f11d55dddfca41544e4b746c8dedb3abe 100644
--- a/pkg/compiler/lib/src/constants/constant_constructors.dart
+++ b/pkg/compiler/lib/src/constants/constant_constructors.dart
@@ -287,18 +287,18 @@ class ConstantConstructorComputer extends SemanticVisitor
 
   @override
   ConstantExpression visitStaticFieldGet(Send node, FieldElement field, _) {
-    return new VariableConstantExpression(field);
+    return new FieldConstantExpression(field);
   }
 
   @override
   ConstantExpression visitTopLevelFunctionGet(
       Send node, MethodElement method, _) {
-    return new FunctionConstantExpression(method);
+    return new FunctionConstantExpression(method, method.type);
   }
 
   @override
   ConstantExpression visitTopLevelFieldGet(Send node, FieldElement field, _) {
-    return new VariableConstantExpression(field);
+    return new FieldConstantExpression(field);
   }
 
   @override