Make ANGLE_texture_usage enableable.

BUG=angleproject:1523

Change-Id: I4e6e4ec6ae7cfb616869373b62dc455d0c5c8c09
Reviewed-on: https://chromium-review.googlesource.com/744444
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/libANGLE/validationES.cpp b/src/libANGLE/validationES.cpp
index 4a19e9a..392b015 100644
--- a/src/libANGLE/validationES.cpp
+++ b/src/libANGLE/validationES.cpp
@@ -5403,6 +5403,12 @@
             break;
 
         case GL_TEXTURE_USAGE_ANGLE:
+            if (!context->getExtensions().textureUsage)
+            {
+                ANGLE_VALIDATION_ERR(context, InvalidEnum(), EnumNotSupported);
+                return false;
+            }
+
             switch (ConvertToGLenum(params[0]))
             {
                 case GL_NONE: