Arrow functions: Cleanup handling of the prototype property

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index ae80021dd6f83283ba1d8c1fbc3d154db1efbd1a..ac25e48853080f384600f0417e9073aba50daa69 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -559,7 +559,7 @@ class Context: public FixedArray {
                                    : STRICT_GENERATOR_FUNCTION_MAP_INDEX;
     }
 
-    if (IsConciseMethod(kind)) {
+    if (IsArrowFunction(kind) || IsConciseMethod(kind)) {
       return strict_mode == SLOPPY
                  ? SLOPPY_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX
                  : STRICT_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX;