Allow empty first parts of ConsStrings

src/objects.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <memory>
 #include <sstream>
@@ skipping 11074 matching lines @@
     cons_string = ConsString::cast(string);
     PushRight(cons_string);
     // Need to traverse all the way left.
     while (true) {
       // Continue left.
       string = cons_string->first();
       type = string->map()->instance_type();
       if ((type & kStringRepresentationMask) != kConsStringTag) {
         AdjustMaximumDepth();
         int length = string->length();
-        DCHECK(length != 0);
+        if (length == 0) break;  // Skip empty left-hand sides of ConsStrings.
         consumed_ += length;
         return string;
       }
       cons_string = ConsString::cast(string);
       PushLeft(cons_string);
     }
   }
   UNREACHABLE();
   return NULL;
 }
@@ skipping 8789 matching lines @@
             .is_null()) {
       return false;
     }
   }
 
   return true;
 }
 
 }  // namespace internal
 }  // namespace v8