dart2js cps: Refactor and optimize string concatenations.

pkg/compiler/lib/src/js_backend/codegen/unsugar.dart

Index: pkg/compiler/lib/src/js_backend/codegen/unsugar.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/unsugar.dart b/pkg/compiler/lib/src/js_backend/codegen/unsugar.dart
index 045e7664a039764ab37e32a628d66fd21b20b9d9..494828e8cd9909f5cf028e6b0dcf70559fb74ff0 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/unsugar.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/unsugar.dart
@@ -82,21 +82,15 @@ class UnsugarVisitor extends RecursiveVisitor {
   }
 
   Constant get trueConstant {
-    return new Constant(
-        new BoolConstantExpression(true),
-        new TrueConstantValue());
+    return new Constant(new TrueConstantValue());
   }
 
   Constant get falseConstant {
-    return new Constant(
-        new BoolConstantExpression(false),
-        new FalseConstantValue());
+    return new Constant(new FalseConstantValue());
   }
 
   Constant get nullConstant {
-    return new Constant(
-        new NullConstantExpression(),
-        new NullConstantValue());
+    return new Constant(new NullConstantValue());
   }
 
   void insertLetPrim(Primitive primitive, Expression node) {