Merged r11533, r11570 into 3.10 branch.

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index 0f79510d9fcf2b0ac77dbc9e12bfc2bd931ab925..84a0c3d19caa095907d5076bf54a3a99876464df 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -412,12 +412,17 @@ static inline MaybeObject* EnsureJSArrayWithWritableFastElements(
   HeapObject* elms = array->elements();
   Map* map = elms->map();
   if (map == heap->fixed_array_map()) {
-    if (args == NULL || !array->HasFastSmiOnlyElements()) {
+    if (args == NULL || array->HasFastElements()) return elms;
+    if (array->HasFastDoubleElements()) {
+      ASSERT(elms == heap->empty_fixed_array());
+      MaybeObject* maybe_transition =
+          array->TransitionElementsKind(FAST_ELEMENTS);
+      if (maybe_transition->IsFailure()) return maybe_transition;
       return elms;
     }
   } else if (map == heap->fixed_cow_array_map()) {
     MaybeObject* maybe_writable_result = array->EnsureWritableFastElements();
-    if (args == NULL || !array->HasFastSmiOnlyElements() ||
+    if (args == NULL || array->HasFastElements() ||
         maybe_writable_result->IsFailure()) {
       return maybe_writable_result;
     }