Replace tagged keys for fast access by smi, and use smi in boundscheck.

src/ia32/lithium-ia32.h

Index: src/ia32/lithium-ia32.h
diff --git a/src/ia32/lithium-ia32.h b/src/ia32/lithium-ia32.h
index 47d8601cdb0139ddc5d02fadd67ddc382f35c2ae..6712e760e5ee27bb8d1abbfdf658d116de359d90 100644
--- a/src/ia32/lithium-ia32.h
+++ b/src/ia32/lithium-ia32.h
@@ -1596,7 +1596,7 @@ inline static bool ExternalArrayOpRequiresTemp(
   // Operations that require the key to be divided by two to be converted into
   // an index cannot fold the scale operation into a load and need an extra
   // temp register to do the work.
-  return key_representation.IsTagged() &&
+  return key_representation.IsSmi() &&
       (elements_kind == EXTERNAL_BYTE_ELEMENTS ||
        elements_kind == EXTERNAL_UNSIGNED_BYTE_ELEMENTS ||
        elements_kind == EXTERNAL_PIXEL_ELEMENTS);