Unless otherwise noted, changes described below apply to the newest Chrome Beta channel release for Android, Chrome OS, Linux, Mac, and Windows.Custom Elements V1Complex user interfaces often require a large amount of HTML. Most languages allow developers to create their own components built on top of language primitives to mitigate this kind of verbosity. Custom elements allow developers to create their own custom HTML tags, and define the new element’s API and behavior in JavaScript. This enables a browser-native way to build reusable, interoperable components. Chrome 54 provides support for the latest custom elements V1 spec, which is broadly agreed-upon by major browser vendors. Chrome will also continue to support the V0 API until enough developers have moved to V1.BroadcastChannelIt is not uncommon for desktop users to have multiple windows or tabs open simultaneously. Some sites utilize this behavior, such as web editors that open documents in their own tabs. Historically, communicating between those tabs has been difficult. BroadcastChannel is a new one-to-many messaging API between windows, tabs, iframes, web workers, and service workers. It allows scripts to establish named channels to send messages between browsing contexts of the same origin.Media platform improvements on Chrome for AndroidMedia is an increasingly large and important part of the browsing experience on mobile devices that requires fluidly utilizing the entire screen. Developers can now use Element.requestFullScreen() to trigger full screen mode after a screen orientation change in addition to after a user gesture. This allows experiences like rotate-to-fullscreen for media players.  In addition to fullscreen improvements, Chrome on Android now persists the media notification of a backgrounded HTMLVideoElement, allowing a user to continue playing videos while they aren’t visible. Developers can detect background video playback by using the Page Visibility API. Playing background videos in Chrome 54.Other features in this releaseNavigations initiated in an unload handler will be blocked and any prior navigation will continue.The imageSmoothingQuality attribute for CanvasRenderingContext2D allows developers to balance performance and image quality by adjusting resolution when scaling. Sites can use Node.getRootNode(options) to obtain the root for a given node.Using PushSubscription.options, sites can track applicationServerKeys without having to store them offline.The Resource Timing API now supports transfer, encoded, and decoded size attributes, allowing developers to measure cache hit rates and byte usage.The user-select property enables developers to specify which elements can be selected by the user and how.Foreign Fetch and WebUSB are available for experimentation as origin trials.The text-size-adjust property allows sites to control whether font size automatically scales on mobile devices.Deprecations and interoperability improvementsTo match behavior in other browsers, embedded YouTube Flash players will be rewritten by Chrome to use the HTML5 embed style, improving performance and security on Chrome Desktop.CacheQueryOptions now conforms to spec across all CacheStorage methods.initTouchEvent has been removed in favor of the new TouchEvent() constructor.SVGZoomEvent has been removed as it is no longer part of the SVG 2.0 spec.SVGSVGElement.currentView, SVGSVGElement.useCurrentView, SVGViewSpec interface, and SVGSVGElement.viewport have been removed as they are no longer part of the SVG 2.0 spec.SVGTests.requiredFeatures attribute has been deprecated since it no longer provides useful functionality in the SVG 2.0 spec. SVGElement now supports the dataset property.The KeyEvent.keyIdentifier field has been removed in favor of the KeyboardEvent.key field.window.external.IsSearchProviderInstalled() and AddSearchProvider() are now no-ops, since they are unsupported in most other browsers.Posted by Marijn Kruisselbrink, Broadcast Buccaneer
Source: Chromium Blog