Reorganize object type enum, such that proxies are no longer in the middle

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index bb24a2f8544ef73e069031be3bd38c0ed6315855..81886e07424d0c19082c1833b0b5097803c4e2f7 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -509,20 +509,23 @@ Failure* Failure::cast(MaybeObject* obj) {
 
 
 bool Object::IsJSReceiver() {
+  STATIC_ASSERT(LAST_JS_RECEIVER_TYPE == LAST_TYPE);
   return IsHeapObject() &&
       HeapObject::cast(this)->map()->instance_type() >= FIRST_JS_RECEIVER_TYPE;
 }
 
 
 bool Object::IsJSObject() {
-  return IsJSReceiver() && !IsJSProxy();
+  STATIC_ASSERT(LAST_JS_OBJECT_TYPE == LAST_TYPE);
+  return IsHeapObject() &&
+      HeapObject::cast(this)->map()->instance_type() >= FIRST_JS_OBJECT_TYPE;
 }
 
 
 bool Object::IsJSProxy() {
-  return Object::IsHeapObject() &&
-     (HeapObject::cast(this)->map()->instance_type() == JS_PROXY_TYPE ||
-      HeapObject::cast(this)->map()->instance_type() == JS_FUNCTION_PROXY_TYPE);
+  if (!Object::IsHeapObject()) return false;
+  InstanceType type = HeapObject::cast(this)->map()->instance_type();
+  return FIRST_JS_PROXY_TYPE <= type && type <= LAST_JS_PROXY_TYPE;
 }