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/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index 1b2d13c..a9e1be1 100644
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -404,6 +404,7 @@
         case kRGBA_4444_GrPixelConfig:          return true;
         case kRGBA_8888_GrPixelConfig:          return true;
         case kRGB_888_GrPixelConfig:            return false;
+        case kRG_88_GrPixelConfig:              return false;
         case kBGRA_8888_GrPixelConfig:          return true;
         case kSRGBA_8888_GrPixelConfig:         return true;
         case kSBGRA_8888_GrPixelConfig:         return true;
@@ -430,6 +431,7 @@
         case GrColorType::kABGR_4444:    return true;
         case GrColorType::kRGBA_8888:    return true;
         case GrColorType::kRGB_888x:     return false;
+        case GrColorType::kRG_88:        return false;
         case GrColorType::kBGRA_8888:    return true;
         case GrColorType::kRGBA_1010102: return true;
         case GrColorType::kGray_8:       return false;