Add RG_88 texture format

Bug: skia:7903
Change-Id: I69b65fc1cfcc2cc5045bb3b75395f9a256ade278
Reviewed-on: https://skia-review.googlesource.com/c/172979
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
diff --git a/tests/GrSurfaceTest.cpp b/tests/GrSurfaceTest.cpp
index 693fc54..39cfbc4 100644
--- a/tests/GrSurfaceTest.cpp
+++ b/tests/GrSurfaceTest.cpp
@@ -86,6 +86,7 @@
         kRGBA_4444_GrPixelConfig,
         kRGBA_8888_GrPixelConfig,
         kRGB_888_GrPixelConfig,
+        kRG_88_GrPixelConfig,
         kBGRA_8888_GrPixelConfig,
         kSRGBA_8888_GrPixelConfig,
         kSBGRA_8888_GrPixelConfig,