Remove some uses of MaybeObject methods.

src/isolate.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 875 matching lines @@
 Failure* Isolate::ReThrow(Object* exception) {
   bool can_be_caught_externally = false;
   bool catchable_by_javascript = is_catchable_by_javascript(exception);
   ShouldReportException(&can_be_caught_externally, catchable_by_javascript);
 
   thread_local_top()->catcher_ = can_be_caught_externally ?
       try_catch_handler() : NULL;
 
   // Set the exception being re-thrown.
   set_pending_exception(exception);
-  if (exception->IsFailure()) return exception->ToFailureUnchecked();
   return Failure::Exception();
 }
 
 
 Failure* Isolate::ThrowIllegalOperation() {
   if (FLAG_stack_trace_on_illegal) PrintStack(stdout);
   return Throw(heap_.illegal_access_string());
 }
 
 
@@ skipping 1356 matching lines @@
       Handle<JSObject> obj = factory()->NewJSObjectFromMap(map);
       JSObject::NormalizeProperties(obj, KEEP_INOBJECT_PROPERTIES, 8);
       JSObject::SetProperty(registry, name, obj, NONE, STRICT).Assert();
     }
   }
   return Handle<JSObject>::cast(factory()->symbol_registry());
 }
 
 
 } }  // namespace v8::internal