Revert of Replace PushIfAbsent by a Stack object and move StringBuilderJoin to JS

src/runtime/runtime-array.cc

Index: src/runtime/runtime-array.cc
diff --git a/src/runtime/runtime-array.cc b/src/runtime/runtime-array.cc
index a0b3080a092a4a1fa910338cfb18914038e601e6..52d921885da1f6009cc4c9504b0dff65c6f80123 100644
--- a/src/runtime/runtime-array.cc
+++ b/src/runtime/runtime-array.cc
@@ -85,6 +85,29 @@
   CONVERT_ARG_HANDLE_CHECKED(Map, map, 1);
   JSObject::TransitionElementsKind(array, map->elements_kind());
   return *array;
+}
+
+
+// Push an object unto an array of objects if it is not already in the
+// array.  Returns true if the element was pushed on the stack and
+// false otherwise.
+RUNTIME_FUNCTION(Runtime_PushIfAbsent) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 2);
+  CONVERT_ARG_HANDLE_CHECKED(JSArray, array, 0);
+  CONVERT_ARG_HANDLE_CHECKED(JSReceiver, element, 1);
+  RUNTIME_ASSERT(array->HasFastSmiOrObjectElements());
+  int length = Smi::cast(array->length())->value();
+  FixedArray* elements = FixedArray::cast(array->elements());
+  for (int i = 0; i < length; i++) {
+    if (elements->get(i) == *element) return isolate->heap()->false_value();
+  }
+
+  // Strict not needed. Used for cycle detection in Array join implementation.
+  RETURN_FAILURE_ON_EXCEPTION(
+      isolate, JSObject::AddDataElement(array, length, element, NONE));
+  JSObject::ValidateElements(array);
+  return isolate->heap()->true_value();
 }