Ensure capacity when adding parts in String.replace.

src/runtime.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3110 matching lines @@
 
     // Only continue checking for global regexps.
     if (!is_global) break;
 
     current_match = global_cache.FetchNext();
   } while (current_match != NULL);
 
   if (global_cache.HasException()) return Failure::Exception();
 
   if (prev < subject_length) {
+    builder.EnsureCapacity(2);
     builder.AddSubjectSlice(prev, subject_length);
   }
 
   RegExpImpl::SetLastMatchInfo(last_match_info,
                                subject,
                                capture_count,
                                global_cache.LastSuccessfulMatch());
 
   return *(builder.ToString());
 }
@@ skipping 10205 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal