Proxies: Make 'with' work, plus minor other fixes

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 97c1d416bc718926900007757826318f1997dda3..b8e9bde44d708950589cef75eaa9188476831540 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -5847,7 +5847,7 @@ MaybeObject* Heap::AllocateCatchContext(JSFunction* function,
 
 MaybeObject* Heap::AllocateWithContext(JSFunction* function,
                                        Context* previous,
-                                       JSObject* extension) {
+                                       JSReceiver* extension) {
   Object* result;
   { MaybeObject* maybe_result = AllocateFixedArray(Context::MIN_CONTEXT_SLOTS);
     if (!maybe_result->ToObject(&result)) return maybe_result;