Add kRG_88_SkColorType

Bug: skia:9121

Change-Id: Id2a12a5d607b84ce393d2b58233bf8e23f646059
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/235797
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Mike Reed <reed@google.com>
diff --git a/src/gpu/SkGr.cpp b/src/gpu/SkGr.cpp
index fd63056..af99ad8 100644
--- a/src/gpu/SkGr.cpp
+++ b/src/gpu/SkGr.cpp
@@ -257,6 +257,8 @@
             return kRGBA_half_GrPixelConfig;
         case kRGBA_F32_SkColorType:
             return kRGBA_float_GrPixelConfig;
+        case kRG_88_SkColorType:
+            return kRG_88_GrPixelConfig;
     }
     SkASSERT(0);    // shouldn't get here
     return kUnknown_GrPixelConfig;