| KeyedService is a layered component | |
| (https://sites.google.com/a/chromium.org/dev/developers/design-documents/layered-components-design) | |
| to enable it to be shared cleanly on iOS. | |
| This component has the following structure: | |
| - core/: shared code that does not depend on src/content/ or src/ios/ | |
| - content/: Code based on the content layer. | |
| - ios/: Code based on src/ios. |