[ic] Simplify handling of primitive maps.

src/lookup.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/lookup.h"
 
 #include "src/bootstrapper.h"
 #include "src/deoptimizer.h"
 #include "src/elements.h"
 #include "src/field-type.h"
@@ skipping 111 matching lines @@
   // the wrapper. Hence we can skip generating the wrapper for all other cases.
   if (index != kMaxUInt32 && receiver->IsString() &&
       index < static_cast<uint32_t>(String::cast(*receiver)->length())) {
     // TODO(verwaest): Speed this up. Perhaps use a cached wrapper on the native
     // context, ensuring that we don't leak it into JS?
     Handle<JSFunction> constructor = isolate->string_function();
     Handle<JSObject> result = isolate->factory()->NewJSObject(constructor);
     Handle<JSValue>::cast(result)->set_value(*receiver);
     return result;
   }
-  auto root = handle(receiver->GetRootMap(isolate)->prototype(), isolate);
+  auto root =
+      handle(receiver->GetPrototypeChainRootMap(isolate)->prototype(), isolate);
   if (root->IsNull(isolate)) {
     unsigned int magic = 0xbbbbbbbb;
     isolate->PushStackTraceAndDie(magic, *receiver, NULL, magic);
   }
   return Handle<JSReceiver>::cast(root);
 }
 
 
 Handle<Map> LookupIterator::GetReceiverMap() const {
   if (receiver_->IsNumber()) return factory()->heap_number_map();
@@ skipping 693 matching lines @@
                                       : access_check_info->named_interceptor();
     if (interceptor) {
       return handle(InterceptorInfo::cast(interceptor), isolate_);
     }
   }
   return Handle<InterceptorInfo>();
 }
 
 }  // namespace internal
 }  // namespace v8