Support r"xxx" raw strings

runtime/vm/scanner.cc

 // 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.
 
 #include "vm/scanner.h"
 
 #include "platform/assert.h"
 #include "vm/flags.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
@@ skipping 813 matching lines @@
       case ',':
         Recognize(Token::kCOMMA);
         break;
 
       case '@':
         Recognize(Token::kAT);
         if ((c0_ == '"') || (c0_ == '\'')) {
           ScanLiteralString(true);
         }
         break;
+
+      case 'r':
+        if ((LookaheadChar(1) == '"') || (LookaheadChar(1) == '\'')) {
+          ReadChar();
+          ScanLiteralString(true);
+        } else {
+          ScanIdent();
+        }
+        break;
+
       case '"':
       case '\'':
         ScanLiteralString(false);
         break;
 
       case '#':
         ScanLibraryTag();
         break;
 
       default:
@@ skipping 103 matching lines @@
               "%c%#"Px"", kPrivateKeySeparator, key_value);
   const String& result = String::Handle(String::New(private_key, Heap::kOld));
   return result.raw();
 }
 
 
 void Scanner::InitOnce() {
 }
 
 }  // namespace dart