Fix natives fuzzing: Let the StringIndexOf runtime function...

src/runtime.cc

 // Copyright 2006-2008 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 1383 matching lines @@
   HandleScope scope;  // create a new handle scope
   ASSERT(args.length() == 3);
 
   CONVERT_ARG_CHECKED(String, sub, 0);
   CONVERT_ARG_CHECKED(String, pat, 1);
 
   Object* index = args[2];
   uint32_t start_index;
   if (!Array::IndexFromObject(index, &start_index)) return Smi::FromInt(-1);
 
+  RUNTIME_ASSERT(start_index <= static_cast<uint32_t>(sub->length()));
   int position = Runtime::StringMatch(sub, pat, start_index);
   return Smi::FromInt(position);
 }
 
 
 static Object* Runtime_StringLastIndexOf(Arguments args) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 3);
 
   CONVERT_CHECKED(String, sub, args[0]);
@@ skipping 4390 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     Counters::gc_last_resort_from_js.Increment();
     Heap::CollectAllGarbage();
   }
 }
 
 
 } }  // namespace v8::internal