Bailout for %_FastOneByteArrayJoin again.

src/runtime/runtime-array.cc

 // Copyright 2014 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/v8.h"
 
 #include "src/arguments.h"
 #include "src/runtime/runtime-utils.h"
 
 namespace v8 {
@@ skipping 1320 matching lines @@
 
 
 RUNTIME_FUNCTION(Runtime_HasCachedArrayIndex) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 1);
   return isolate->heap()->false_value();
 }
 
 
 RUNTIME_FUNCTION(Runtime_GetCachedArrayIndex) {
-  SealHandleScope shs(isolate);
-  DCHECK(args.length() == 1);
-  return isolate->heap()->undefined_value();
+  // This can never be reached, because Runtime_HasCachedArrayIndex always
+  // returns false.
+  UNIMPLEMENTED();
+  return nullptr;
 }
 
 
 RUNTIME_FUNCTION(Runtime_FastOneByteArrayJoin) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 2);
+  // Returning undefined means that this fast path fails and one has to resort
+  // to a slow path.
   return isolate->heap()->undefined_value();
 }
 }
 }  // namespace v8::internal