Disable compile_xcassets on macOS.

xcassets are only used on iOS, not macOS. We want to minimize the number of
Xcode-based tools used by the macOS toolchain, so we intentionally disallow
future uses of xcassets on macOS.

Change-Id: Id559f84633be6c935211561b976a7991810d94ad
Bug: 965663
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1643406
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#666695}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 6c478646f25b58fe24c885b76f3f3e5c0a0fcd51

toolchain/mac/BUILD.gn

@@ -440,6 +440,11 @@ template("mac_toolchain") {
       description = "COPY_BUNDLE_DATA {{source}} {{output}}"
       pool = ":bundle_pool($default_toolchain)"
     }
+
+    # xcassets are only used on iOS, not macOS. We want to minimize the number
+    # of Xcode-based tools used by the macOS toolchain, so we intentionally
+    # disallow future uses of xcassets on macOS. https://crbug.com/965663.
+    if (toolchain_args.current_os == "ios") {
       tool("compile_xcassets") {
         _tool = rebase_path("//build/toolchain/mac/compile_xcassets.py",
                             root_build_dir)
@@ -462,6 +467,7 @@ template("mac_toolchain") {
         description = "COMPILE_XCASSETS {{output}}"
         pool = ":bundle_pool($default_toolchain)"
       }
+    }
 
     tool("action") {
       pool = "//build/toolchain:action_pool($default_toolchain)"