Implement EXT_blend_minmax.

BUG=angle:555

Change-Id: I1ae6a9783e718d16ee08bda5463f11cd52ad0967
Reviewed-on: https://chromium-review.googlesource.com/186123
Tested-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
diff --git a/src/libGLESv2/Context.cpp b/src/libGLESv2/Context.cpp
index 6b91d91..8322d7e 100644
--- a/src/libGLESv2/Context.cpp
+++ b/src/libGLESv2/Context.cpp
@@ -3710,6 +3710,7 @@
 
         mExtensionStringList.push_back("GL_EXT_texture_storage");
         mExtensionStringList.push_back("GL_EXT_frag_depth");
+        mExtensionStringList.push_back("GL_EXT_blend_minmax");
 
         // ANGLE-specific extensions
         if (supportsDepthTextures())