Implement cascade operator in VM

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 755 matching lines @@
         if (c0_ == '=') {
           Recognize(Token::kEQ);
           if (c0_ == '=') {
             Recognize(Token::kEQ_STRICT);
           }
         } else if (c0_ == '>') {
           Recognize(Token::kARROW);
         }
         break;
 
-      case '.':  // .  Number
+      case '.':  // .  ..  Number
         Recognize(Token::kPERIOD);
-        if (IsDecimalDigit(c0_)) {
+        if (c0_ == '.') {
+          Recognize(Token::kCASCADE);
+        } else if (IsDecimalDigit(c0_)) {
           ScanNumber(true);
         }
         break;
 
       case '?':
         Recognize(Token::kCONDITIONAL);
         break;
 
       case ':':
         Recognize(Token::kCOLON);
@@ skipping 156 matching lines @@
               "%c%"PRIxPTR, kPrivateKeySeparator, key_value);
   const String& result = String::Handle(String::New(private_key, Heap::kOld));
   return result.raw();
 }
 
 
 void Scanner::InitOnce() {
 }
 
 }  // namespace dart