web.performance interfaces.

The Navigator interface represents the state and the identity
the user agent. It allows scripts to query it and to register
to carry on some activities.

The Performance interface provides access to performance-related
for the current page. It's part of the High Resolution Time API,
is enhanced by the Performance Timeline API, the Navigation Timing
the User Timing API, and the Resource Timing API.

Performance Events.

The PerformanceEntry object encapsulates a single performance
that is part of the performance timeline. A performance entry
be directly created by making a performance `mark` or `measure`
example by calling the `mark()` method) at an explicit point
an application. Performance entries are also created in indirect
such as loading a resource (such as an image).

PerformanceFrameTiming is an abstract interface that provides
timing data about the browser's event loop.

PerformanceMark is an abstract interface for `web.performance.PerformanceEntry`
with an `entryType` of \"mark\". Entries of this type are created
calling `performance.mark()` to add a named `web.dom.DOMHighResTimeStamp`
mark) to the browser's performance timeline.

PerformanceMeasure is an abstract interface for `web.performance.PerformanceEntry`
with an `entryType` of \"measure\". Entries of this type are
by calling `performance.measure()` to add a named `web.dom.DOMHighResTimeStamp`
measure) between two marks to the browser's performance timeline.

The PerformanceNavigationTiming interface provides methods and
to store and retrieve metrics regarding the browser's document
events. For example, this interface can be used to determine
much time it takes to load or unload a document.

The PerformanceObserverEntryList interface is a list of peformance
that were explicitly observed via the `observe()` method.

The PerformancePaintTiming interface of the Paint Timing provides
information about \"paint\" (also called \"render\") operations
web page construction. \"Paint\" refers to conversion of the
tree to on-screen pixels.

The PerformanceResourceTiming interface enables retrieval and
of detailed network timing data regarding the loading of an application's
An application can use the timing metrics to determine, for example,
length of time it takes to fetch a specific resource, such as
`web.XMLHttpRequest`, `<SVG>`, image, or script.

The PerformanceServerTiming interface surfaces server metrics
are sent with the response in the `Server-Timing` HTTP header.