[builtins] Migrate Object.keys to C++.

src/execution.h

 // 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.
 
 #ifndef V8_EXECUTION_H_
 #define V8_EXECUTION_H_
 
 #include "src/allocation.h"
 #include "src/base/atomicops.h"
 #include "src/handles.h"
@@ skipping 32 matching lines @@
   // calling the function (if caught exception is false) or the exception
   // that occurred (if caught exception is true).
   // In the exception case, exception_out holds the caught exceptions, unless
   // it is a termination exception.
   static MaybeHandle<Object> TryCall(Isolate* isolate, Handle<Object> callable,
                                      Handle<Object> receiver, int argc,
                                      Handle<Object> argv[],
                                      MaybeHandle<Object>* exception_out = NULL);
 
   // ECMA-262 9.9
-  MUST_USE_RESULT static MaybeHandle<Object> ToObject(
-      Isolate* isolate, Handle<Object> obj);
+  MUST_USE_RESULT static MaybeHandle<JSReceiver> ToObject(Isolate* isolate,
+                                                          Handle<Object> obj);
 
   static Handle<String> GetStackTraceLine(Handle<Object> recv,
                                           Handle<JSFunction> fun,
                                           Handle<Object> pos,
                                           Handle<Object> is_global);
 };
 
 
 class ExecutionAccess;
 class PostponeInterruptsScope;
@@ skipping 164 matching lines @@
   friend class StackLimitCheck;
   friend class PostponeInterruptsScope;
 
   DISALLOW_COPY_AND_ASSIGN(StackGuard);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_EXECUTION_H_