Experimental: Add R_16 and RG_1616 to Ganesh (take 2)

This is to support the P016 and P010 YUV formats. Initially, only Vulkan and GL support these formats.

Change-Id: I4e896f1d3fb32207227a755517ae5a00a58e6045
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/219403
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/src/gpu/gl/GrGLVertexArray.cpp b/src/gpu/gl/GrGLVertexArray.cpp
index 00d7d8d..4e6346d 100644
--- a/src/gpu/gl/GrGLVertexArray.cpp
+++ b/src/gpu/gl/GrGLVertexArray.cpp
@@ -74,6 +74,9 @@
             return {false, 1, GR_GL_INT};
         case kUint_GrVertexAttribType:
             return {false, 1, GR_GL_UNSIGNED_INT};
+        // Experimental (for P016 and P010)
+        case kUShort_norm_GrVertexAttribType:
+            return {true, 1, GR_GL_UNSIGNED_SHORT};
     }
     SK_ABORT("Unknown vertex attrib type");
     return {false, 0, 0};