[proxies] Implement [[Delete]].

src/bootstrapper.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/bootstrapper.h"
 
 #include "src/accessors.h"
 #include "src/api-natives.h"
 #include "src/code-stubs.h"
 #include "src/extensions/externalize-string-extension.h"
@@ skipping 669 matching lines @@
     Builtins::Name builtin_name) {
   Handle<String> name =
       factory()->InternalizeOneByteString(STATIC_CHAR_VECTOR("ThrowTypeError"));
   Handle<Code> code(isolate()->builtins()->builtin(builtin_name));
   Handle<JSFunction> function =
       factory()->NewFunctionWithoutPrototype(name, code);
   function->set_map(native_context()->sloppy_function_map());
   function->shared()->DontAdaptArguments();
 
   // %ThrowTypeError% must not have a name property.
-  JSReceiver::DeleteProperty(function, factory()->name_string()).Assert();
+  if (JSReceiver::DeleteProperty(function, factory()->name_string())
+          .IsNothing())
+    DCHECK(false);
 
   // length needs to be non configurable.
   Handle<Object> value(Smi::FromInt(function->shared()->length()), isolate());
   JSObject::SetOwnPropertyIgnoreAttributes(
       function, factory()->length_string(), value,
       static_cast<PropertyAttributes>(DONT_ENUM | DONT_DELETE | READ_ONLY))
       .Assert();
 
   if (JSObject::PreventExtensions(function, Object::THROW_ON_ERROR).IsNothing())
     DCHECK(false);
@@ skipping 2557 matching lines @@
 }
 
 
 // Called when the top-level V8 mutex is destroyed.
 void Bootstrapper::FreeThreadResources() {
   DCHECK(!IsActive());
 }
 
 }  // namespace internal
 }  // namespace v8