Refactor BackendHelpers to be reusageable with KernelWorldBuilder

pkg/compiler/lib/src/string_validator.dart

 // Copyright (c) 2012, 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.
 
 // Check the validity of string literals.
 
 library stringvalidator;
 
 import 'dart:collection';
 
@@ skipping 81 matching lines @@
    * literals (including an initial 'r' for raw strings).
    */
   String copyWithoutQuotes(String string, int initial, int terminal) {
     assert(0 <= initial);
     assert(0 <= terminal);
     assert(initial + terminal <= string.length);
     return string.substring(initial, string.length - terminal);
   }
 
   void stringParseError(String message, Token token, int offset) {
-    reporter.reportErrorMessage(
-        reporter.spanFromToken(token), MessageKind.GENERIC,
-        {'text': "$message @ $offset"});
+    reporter.reportErrorMessage(reporter.spanFromToken(token),
+        MessageKind.GENERIC, {'text': "$message @ $offset"});
   }
 
   /**
    * Validates the escape sequences and special characters of a string literal.
    * Returns a DartString if valid, and null if not.
    */
   DartString validateString(
       Token token, int startOffset, String string, StringQuoting quoting) {
     // We need to check for invalid x and u escapes, for line
     // terminators in non-multiline strings, and for invalid Unicode
@@ skipping 91 matching lines @@
       }
     }
     // String literal successfully validated.
     if (quoting.raw || !containsEscape) {
       // A string without escapes could just as well have been raw.
       return new DartString.rawString(string, length);
     }
     return new DartString.escapedString(string, length);
   }
 }