cps-ir: Implement string concatenation.

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

 // Copyright (c) 2014, 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 code_generator_dependencies;
 
 import '../js_backend.dart';
 import '../../dart2jslib.dart';
 import '../../js_emitter/js_emitter.dart';
 import '../../js/js.dart' as js;
@@ skipping 12 matching lines @@
 
   CodeEmitterTask get _emitter => _backend.emitter;
   Namer get _namer => _backend.namer;
 
   Glue(this._compiler);
 
   js.Expression constantReference(ConstantValue value) {
     return _emitter.constantReference(value);
   }
 
+  Element getStringConversion() {
+    return _backend.getStringInterpolationHelper();
+  }
+
   reportInternalError(String message) {
     _compiler.internalError(_compiler.currentElement, message);
   }
 
   ConstantExpression getConstantForVariable(VariableElement variable) {
     return _backend.constants.getConstantForVariable(variable);
   }
 
   js.Expression staticFunctionAccess(Element element) {
     return _backend.emitter.staticFunctionAccess(element);
@@ skipping 53 matching lines @@
     return _namer.instanceMethodName(element);
   }
 
   js.Expression prototypeAccess(ClassElement e,
                                 {bool hasBeenInstantiated: false}) {
     return _emitter.prototypeAccess(e,
         hasBeenInstantiated: hasBeenInstantiated);
   }
 
 }