Add "has fast elements" bit to maps and use it in inlined keyed loads.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 464ca54d2d4f89eaa71a9e87d62372562b643d51..0f64dd45ec58a165ee3856c5df5ad04e7831e899 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -2606,6 +2606,8 @@ void v8::Object::SetIndexedPropertiesToPixelData(uint8_t* data, int length) {
     return;
   }
   i::Handle<i::PixelArray> pixels = i::Factory::NewPixelArray(length, data);
+  self->set_map(
+      *i::Factory::GetSlowElementsMap(i::Handle<i::Map>(self->map())));
   self->set_elements(*pixels);
 }
 
@@ -2659,6 +2661,8 @@ void v8::Object::SetIndexedPropertiesToExternalArrayData(
   }
   i::Handle<i::ExternalArray> array =
       i::Factory::NewExternalArray(length, array_type, data);
+  self->set_map(
+      *i::Factory::GetSlowElementsMap(i::Handle<i::Map>(self->map())));
   self->set_elements(*array);
 }