This patch adds the declaration of libANGLE/features.h in UniformLinker.cpp
to fix the build failure on Linux when you use gn to build ANGLE alone.

BUG=angleproject:1938

Change-Id: I19636df8f81b307e6d2e08fdac286cfb3f705eab
Reviewed-on: https://chromium-review.googlesource.com/454083Reviewed-by: Yunchao He <yunchao.he@intel.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>