Add support for EXT_YUV_target

Add new sampler type "__samplerExternal2DY2YEXT"
to sample a YUV texture image and output color value
without any color conversion,
new additional type to specify color space standard formula and
built-in functions for yuv to rgb transformation.

Change-Id: I1780650fe84cd75191c1ca1e4118e89d585bfd92
Reviewed-on: https://chromium-review.googlesource.com/454697
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/compiler/translator/ShaderLang.cpp b/src/compiler/translator/ShaderLang.cpp
index fe7c71d..11b83f3 100644
--- a/src/compiler/translator/ShaderLang.cpp
+++ b/src/compiler/translator/ShaderLang.cpp
@@ -163,6 +163,7 @@
     resources->NV_shader_framebuffer_fetch     = 0;
     resources->ARM_shader_framebuffer_fetch    = 0;
     resources->OVR_multiview                   = 0;
+    resources->EXT_YUV_target                  = 0;
 
     resources->NV_draw_buffers = 0;