This patch adds the swizzle process if the swizzle node is the last node in
ssbo access chain.

Bug: angleproject:1951

Change-Id: Iecc95baa45e8cc40be9111a15398c7e858bfb99e
Reviewed-on: https://chromium-review.googlesource.com/c/1341234
Commit-Queue: Jiajia Qin <jiajia.qin@intel.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>