Advertise GL_ANGLE_texture_usage.

TRAC #18732
Signed-off-by: Daniel Koch
Author: Nicolas Capens

git-svn-id: https://angleproject.googlecode.com/svn/trunk@863 736b8ea6-26fd-11df-bfd4-992fa37f6226
diff --git a/src/libGLESv2/Context.cpp b/src/libGLESv2/Context.cpp
index de14e52..a93e376 100644
--- a/src/libGLESv2/Context.cpp
+++ b/src/libGLESv2/Context.cpp
@@ -3445,6 +3445,8 @@
     {
         mExtensionString += "GL_ANGLE_texture_compression_dxt5 ";
     }
+
+    mExtensionString += "GL_ANGLE_texture_usage ";
     mExtensionString += "GL_ANGLE_translated_shader_source ";
 
     // Other vendor-specific extensions