Add ConstantConstructor to ConstantExpression system.

pkg/compiler/lib/src/compile_time_constants.dart

Index: pkg/compiler/lib/src/compile_time_constants.dart
diff --git a/pkg/compiler/lib/src/compile_time_constants.dart b/pkg/compiler/lib/src/compile_time_constants.dart
index c16a09ceba8378ce060892a619fe6d0c31164acc..f9da31435ca5dca9a65e61feff9cbba2eccb75cd 100644
--- a/pkg/compiler/lib/src/compile_time_constants.dart
+++ b/pkg/compiler/lib/src/compile_time_constants.dart
@@ -755,16 +755,6 @@ class CompileTimeConstantEvaluator extends Visitor<AstConstant> {
         constructor == compiler.boolEnvironment ||
         constructor == compiler.stringEnvironment) {
 
-      AstConstant createEvaluatedConstant(ConstantValue value) {
-        return new AstConstant(
-            context, node, new ConstructedConstantExpression(
-                value,
-                type,
-                constructor,
-                elements.getSelector(send).callStructure,
-                concreteArguments.map((e) => e.expression).toList()));
-      }
-
       var firstArgument = normalizedArguments[0].value;
       ConstantValue defaultValue = normalizedArguments[1].value;
 
@@ -809,8 +799,26 @@ class CompileTimeConstantEvaluator extends Visitor<AstConstant> {
         return null;
       }
 
+      String name =
+          firstArgument.primitiveValue.slowToString();
       String value =
-          compiler.fromEnvironment(firstArgument.primitiveValue.slowToString());
+          compiler.fromEnvironment(name);
+
+      AstConstant createEvaluatedConstant(ConstantValue value) {
+
+        ConstantExpression expression;
+        if (constructor == compiler.intEnvironment) {
+          expression = new IntFromEnvironmentConstantExpression(
+              value, name, normalizedArguments[1].expression);
+        } else if (constructor == compiler.boolEnvironment) {
+          expression = new BoolFromEnvironmentConstantExpression(
+              value, name, normalizedArguments[1].expression);
+        } else if (constructor == compiler.stringEnvironment) {
+          expression = new StringFromEnvironmentConstantExpression(
+              value, name, normalizedArguments[1].expression);
+        }
+        return new AstConstant(context, node, expression);
+      }
 
       if (value == null) {
         return createEvaluatedConstant(defaultValue);