Add SkBitmap StructTraits for skia::mojo::Bitmap.

ash/sysui/BUILD.gn

Index: ash/sysui/BUILD.gn
diff --git a/ash/sysui/BUILD.gn b/ash/sysui/BUILD.gn
index 943623c44db564915701c7498f0320195d41e148..caf72649e8c7b6185666b534ae74d26864014c57 100644
--- a/ash/sysui/BUILD.gn
+++ b/ash/sysui/BUILD.gn
@@ -40,12 +40,10 @@ source_set("lib") {
     "//components/mus/public/interfaces",
     "//components/user_manager",
     "//device/bluetooth",
-    "//mash/shelf/public/interfaces",
     "//mojo/common:common_base",
     "//services/catalog/public/cpp",
     "//services/shell/public/cpp",
     "//services/tracing/public/cpp",
-    "//skia/public",
     "//ui/app_list/presenter",
     "//ui/app_list/presenter:mojom",
     "//ui/aura",
@@ -64,6 +62,10 @@ source_set("lib") {
     "//ui/views/mus:for_mojo_application",
   ]
 
+  public_deps = [
+    "//mash/shelf/public/interfaces",
+  ]
+
   if (is_chromeos) {
     deps += [ "//chromeos" ]
   }