Use UnaryOperator and BinaryOperator in ConstantSystem.

pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart

Index: pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart
diff --git a/pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart b/pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart
index 06052a966b77d58284faec0019c4913f1c3cab72..57add3952f53969bb09047fac7cde4dab4e16e5d 100644
--- a/pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart
+++ b/pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart
@@ -1255,6 +1255,12 @@ class ConstantEmitter
   }
 
   @override
+  Expression visitIdentical(IdenticalConstantExpression exp,
+                            BuilderContext<Statement> context) {
+    return handlePrimitiveConstant(exp.value);
+  }
+
+  @override
   Expression visitConditional(ConditionalConstantExpression exp,
                               BuilderContext<Statement> context) {
     if (exp.condition.value.isTrue) {