example builds:
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20ASAN%20Debug/17608
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20ASAN%20Debug/17598
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20ASAN%20Debug/17585

no-op check warned with following logs:
```
ninja explain: output obj/content/shell/content_shell_framework_shared_library_bundle_data.stamp older than most recent input obj/content/shell/content_shell_framework_shared_library/Content Shell Framework (1547449219 vs 1547449305)
ninja explain: obj/content/shell/content_shell_framework_shared_library_bundle_data.stamp is dirty
ninja explain: recorded mtime of Content Shell Framework.framework/Versions/C/Content Shell Framework older than most recent input obj/content/shell/content_shell_framework_shared_library/Content Shell Framework (1547448765 vs 1547449305)
ninja explain: Content Shell Framework.framework/Versions/C/Content Shell Framework is dirty
ninja explain: obj/content/shell/content_shell_framework.stamp is dirty
ninja explain: Content Shell Framework.framework is dirty
ninja explain: Content Shell Framework.framework is dirty
ninja explain: obj/content/shell/content_shell_framework.stamp is dirty
ninja explain: obj/content/shell/content_shell_framework_bundle_data.stamp is dirty
ninja explain: Content Shell.app/Contents/Frameworks/Content Shell Framework.framework is dirty
ninja explain: obj/content/shell/content_shell.stamp is dirty
ninja explain: obj/chromium_builder_asan.stamp is dirty
```

I guess this is basically come from specifying directory instead of enumerating files.
https://cs.chromium.org/chromium/src/content/shell/BUILD.gn?l=849&rcl=06548fb143b21d1ef09cd40509a860b262907ad8


Also may be related to
https://github.com/ninja-build/ninja/issues/1186