Fixed a couple of proxies-related unhandled exceptions.

src/objects.cc

 // Copyright 2013 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 <iomanip>
 #include <sstream>
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 3985 matching lines @@
     writable = isolate->factory()->ToBoolean(!setter->IsUndefined());
   }
 
   if (configurable->IsFalse()) {
     Handle<Object> handler(proxy->handler(), isolate);
     Handle<String> trap = isolate->factory()->InternalizeOneByteString(
         STATIC_CHAR_VECTOR("getPropertyDescriptor"));
     Handle<Object> error = isolate->factory()->NewTypeError(
         MessageTemplate::kProxyPropNotConfigurable, handler, name, trap);
     isolate->Throw(*error);
-    return Just(NONE);
+    return Nothing<PropertyAttributes>();
   }
 
   int attributes = NONE;
   if (!enumerable->BooleanValue()) attributes |= DONT_ENUM;
   if (!configurable->BooleanValue()) attributes |= DONT_DELETE;
   if (!writable->BooleanValue()) attributes |= READ_ONLY;
   return Just(static_cast<PropertyAttributes>(attributes));
 }
 
 
@@ skipping 12114 matching lines @@
                                             Handle<Object> new_value) {
   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