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/ParseContext.h b/src/compiler/translator/ParseContext.h
index 6283d30..66dda7f 100644
--- a/src/compiler/translator/ParseContext.h
+++ b/src/compiler/translator/ParseContext.h
@@ -399,6 +399,8 @@
                                      int objectLocationCount,
                                      const TLayoutQualifier &layoutQualifier);
 
+    void checkYuvIsNotSpecified(const TSourceLoc &location, bool yuv);
+
     TIntermTyped *addBinaryMathInternal(TOperator op,
                                         TIntermTyped *left,
                                         TIntermTyped *right,