Better handle backendFormat to CompressionType.

We also fix getReadSwizzle with this change.

Change-Id: I1989d8347dc97d7a4c75aa9094a0146419c6d8fa
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/295819
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
diff --git a/gn/gpu.gni b/gn/gpu.gni
index 15b9092..d2d4f88 100644
--- a/gn/gpu.gni
+++ b/gn/gpu.gni
@@ -39,6 +39,7 @@
   "$_src/gpu/GrBackendSurfaceMutableStateImpl.h",
   "$_src/gpu/GrBackendTextureImageGenerator.cpp",
   "$_src/gpu/GrBackendTextureImageGenerator.h",
+  "$_src/gpu/GrBackendUtils.h",
   "$_src/gpu/GrBaseContextPriv.h",
   "$_src/gpu/GrBitmapTextureMaker.cpp",
   "$_src/gpu/GrBitmapTextureMaker.h",