dart2js cps: Refactor and optimize string concatenations.

tests/html/html.status

 # Copyright (c) 2013, 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.
 
 interactive_test: Skip # Must be run manually.
 dromaeo_smoke_test: Skip # Issue 14521, 8257
 cross_frame_test: Skip # Test reloads itself. Issue 18558
 
 [ $compiler == none && ($runtime == drt || $runtime == dartium || $runtime == ContentShellOnAndroid) ]
 custom/attribute_changed_callback_test/unsupported_on_polyfill: Fail # Issue 18931 (Disabled for Chrome 35 roll)
@@ skipping 516 matching lines @@
 storage_test: Crash # Invalid argument(s)
 streams_test: Crash # Invalid argument(s)
 svg_test: Crash # (try {body();}catch ...  try/finally
 svgelement_test: Crash # (try {body();}catch ...  try/finally
 table_test: Crash # Invalid argument(s)
 text_event_test: Crash # Invalid argument(s)
 touchevent_test: Crash # (try {body();}catch ...  try/finally
 track_element_constructor_test: Crash # (try {return f(arg1,arg2);}finally {Zone._leave(old);}): try/finally
 transferables_test: Crash # Invalid argument(s)
 transition_event_test: Crash # (try {body();}catch ...  try/finally
+trusted_html_tree_sanitizer_test : Crash # bailout: (try {body();}catch (e,trace){var stack=(trace==null)?'':': ${trace.toString()}';environment.uncaughtErrorMessage="${e.toString()}${stack}";}finally {environment.currentContext=environment.currentContext.parent;}): try/finally
 typed_arrays_1_test: Crash # (try {body();}catch ...  try/finally
 typed_arrays_2_test: Crash # Invalid argument(s)
 typed_arrays_3_test: Crash # Invalid argument(s)
 typed_arrays_4_test: Crash # Invalid argument(s)
 typed_arrays_5_test: Crash # Invalid argument(s)
 typed_arrays_arraybuffer_test: Crash # Invalid argument(s)
 typed_arrays_dataview_test: Crash # Invalid argument(s)
 typed_arrays_range_checks_test: Crash # Invalid argument(s)
 typed_arrays_simd_test: Crash # Invalid argument(s)
 typing_test: Crash # Invalid argument(s)
 unknownelement_test: Crash # Invalid argument(s)
 uri_test: Crash # Invalid argument(s)
 url_test: Crash # (try {body();}catch ...  try/finally
 webgl_1_test: Crash # (try {body();}catch ...  try/finally
 websocket_test: Crash # (try {body();}catch ...  try/finally
 websql_test: Crash # (try {body();}catch ...  try/finally
 wheelevent_test: Crash # (try {return f(arg1,arg2);}finally {Zone._leave(old);}): try/finally
 window_eq_test: Crash # Invalid argument(s)
 window_mangling_test: Crash # Invalid argument(s)
 window_nosuchmethod_test: Crash # Invalid argument(s)
 window_test: Crash # Invalid argument(s)
 worker_api_test: Crash # (try {return f(arg1,arg2);}finally {Zone._leave(old);}): try/finally
 worker_test: Crash # (try {body();}catch ...  try/finally
 xhr_cross_origin_test: Crash # (try {body();}catch ...  try/finally
 xhr_test: Crash # (try {body();}catch ...  try/finally
 xsltprocessor_test: Crash # (try {body();}catch ...  try/finally