public.bzl: add metal_objc_srcs()

Change-Id: I0e2f7a029a5e4a9dc6901eaab1791e8b74ebe29b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/259338
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/public.bzl b/public.bzl
index 0d92a20..87aee5d 100644
--- a/public.bzl
+++ b/public.bzl
@@ -401,6 +401,18 @@
 def skia_srcs(os_conditions):
     return base_srcs() + ports_srcs(os_conditions) + gl_srcs(os_conditions)
 
+def metal_objc_srcs():
+    return native.glob(
+        [
+            "include/**/*.h",
+            "src/**/*.h",
+            "src/gpu/mtl/**/*.mm",
+            "third_party/**/*.h",
+        ]
+    ) + [
+        "src/image/SkSurface_GpuMtl.mm",
+    ]
+
 ################################################################################
 ## INCLUDES
 ################################################################################