Reland "Allocation site support for monomorphic StringAdds in BinaryOps".

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 5975d80fad0c01dc6cfa29e6334f314604ca5906..dbf21d2c833ccf820cf17b103091962005bfc151 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1349,7 +1349,9 @@ AllocationSiteMode AllocationSite::GetMode(ElementsKind from,
 
 inline bool AllocationSite::CanTrack(InstanceType type) {
   if (FLAG_allocation_site_pretenuring) {
-    return type == JS_ARRAY_TYPE || type == JS_OBJECT_TYPE;
+    return type == JS_ARRAY_TYPE ||
+        type == JS_OBJECT_TYPE ||
+        type < FIRST_NONSTRING_TYPE;
   }
   return type == JS_ARRAY_TYPE;
 }