The page load metrics subsystem captures and records UMA metrics related to page loading. This includes page timing metrics, such as time to first paint, as well as page interaction metrics, such as number of page loads aborted before first paint.
The page load metrics subsystem is shared by Chrome and WebView, but not supported on iOS, as it requires hooks into Blink for page timing metrics that are unavailable on iOS.
This component has the following structure and these directories follow the rule that //content follows. If your new file needs to depend on something that //content disallows, you need to consider to place it outside //components/page_load_metrics/, e.g. //chrome/browser/page_load_metrics/ for Chrome, or //components/page_load_metrics/google/ if it depends on Google specific properties and is used from multiple embedders, e.g. Chrome and WebView.
For additional information on this subsystem, see https://docs.google.com/document/d/1HJsJ5W2H_3qRdqPAUgAEo10AF8gXPTXZLUET4X4_sII/edit