Gracefully handle proxies in AllCanWrite().

src/objects.cc

 // Copyright 2015 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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 1348 matching lines @@
   }
   it->isolate()->ReportFailedAccessCheck(checked);
   RETURN_VALUE_IF_SCHEDULED_EXCEPTION(it->isolate(),
                                       Nothing<PropertyAttributes>());
   return Just(ABSENT);
 }
 
 
 // static
 bool JSObject::AllCanWrite(LookupIterator* it) {
-  for (; it->IsFound(); it->Next()) {
+  for (; it->IsFound() && it->state() != LookupIterator::JSPROXY; it->Next()) {
     if (it->state() == LookupIterator::ACCESSOR) {
       Handle<Object> accessors = it->GetAccessors();
       if (accessors->IsAccessorInfo()) {
         if (AccessorInfo::cast(*accessors)->all_can_write()) return true;
       }
     }
   }
   return false;
 }
 
@@ skipping 18270 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8