Enabled loop indexing validation for fragment shaders compiled using renderers configured for FL9_3 and below.

BUG=angleproject:1130

Change-Id: I2b5d7091c394565354b14fbf9297276dce8d92a5
Reviewed-on: https://chromium-review.googlesource.com/294733Tested-by: Cooper Partin <coopp@microsoft.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>