Implements the border-area value for the CSS background-clip property, as defined in CSS Backgrounds Level 4. background-clip: border-area clips an element's background to the area painted by its border strokes, taking border-width and border-style into account while ignoring transparency from border-color. This enables gradient borders without border-image. WebKit already ships this feature; this implementation brings Chromium to parity.
There is currently no ergonomic way to clip a background to the visible border geometry in CSS. Authors who want gradient or image borders must use border-image, which is complex, overrides other border styling, and does not compose well with other properties. The border-area clip value provides a clean, declarative solution to this problem. WebKit already ships this feature, and it is part of the actively developed CSS Backgrounds Level 4 specification.