This directory is for features that are intended for reuse. For example, code that is shared between multiple embedders of ios/web like ios/web_view and ios/chrome. This means that components must not depend on either ios/web_view or ios/chrome.
Code which can be shared across Chrome on all platforms should go in //components (which also supports iOS specific sources).
Code in a component should be placed in a namespace corresponding to the name of the component; e.g. for a component living in //components/foo, code in that component should be in the foo:: namespace.