The unit test uses a test manifest but real file_manager grit resources for testing. It also requires that the relative path of the file_manager icon to match what is defined in the test_manifest (currently common/images/icon16.png) else IsComponentExtensionResource is unable find the resource id in its map.

Refactor the unit test not to depend on real file_manager grit resources.

https://codesearch.chromium.org/chromium/src/chrome/browser/extensions/chrome_component_extension_resource_manager_unittest.cc?rcl=bbc810df20d5b70e320c6ae5be761f9e97f89f6c&l=71