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 3b0e96f1ef93793398b98eb7a5daa50ca1c156a6..8d1adad262ed5e563d3e5fef3fadf7dd132574c7 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);
+     (HeapObject::cast(this)->map()->instance_type() >= FIRST_JS_PROXY_TYPE &&
+      HeapObject::cast(this)->map()->instance_type() <= LAST_JS_PROXY_TYPE);
 }