[runtime] [proxy] Adding [[SetPrototypeOf]] trap.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 23d8038be021ad6b4419a498a34fc29db9b85ab7..306ba0f5e15bc885bcd67b669261b686dc17f8e1 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -9499,6 +9499,11 @@ class JSProxy: public JSReceiver {
   // ES6 9.5.1
   static MaybeHandle<Object> GetPrototype(Handle<JSProxy> receiver);
 
+  // ES6 9.5.2
+  MUST_USE_RESULT static Maybe<bool> SetPrototype(Handle<JSProxy> proxy,
+                                                  Handle<Object> value,
+                                                  bool from_javascript,
+                                                  ShouldThrow should_throw);
   // ES6 9.5.3
   MUST_USE_RESULT static Maybe<bool> IsExtensible(Handle<JSProxy> proxy);