[builtins] WIP: Array indexOf in TurboFan/Runtime

src/elements.h

Index: src/elements.h
diff --git a/src/elements.h b/src/elements.h
index f4b0b0b7c55931b21d8f15c651dbeaa478494bf2..1ffd4d996fbfa4845f61fd9e62c421a352fc6e5e 100644
--- a/src/elements.h
+++ b/src/elements.h
@@ -160,6 +160,13 @@ class ElementsAccessor {
                                     Handle<Object> value, uint32_t start,
                                     uint32_t length) = 0;
 
+  // Check an Object's own elements for the index of an element (using SameValue
+  // semantics)
+  virtual Maybe<int64_t> IndexOfValue(Isolate* isolate,
+                                      Handle<JSObject> receiver,
+                                      Handle<Object> value, uint32_t start,
+                                      uint32_t length) = 0;
+
  protected:
   friend class LookupIterator;