Fix build failure in UniformLinker.cpp on Linux

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/454083
Reviewed-by: Yunchao He <yunchao.he@intel.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/UniformLinker.cpp b/src/libANGLE/UniformLinker.cpp
index 7028303..8b735c4 100644
--- a/src/libANGLE/UniformLinker.cpp
+++ b/src/libANGLE/UniformLinker.cpp
@@ -13,6 +13,7 @@
 #include "common/utilities.h"
 #include "libANGLE/Caps.h"
 #include "libANGLE/Shader.h"
+#include "libANGLE/features.h"
 
 namespace gl
 {