Iframe Layout Coordination and Cooperative Sizing in Blink

The provided text describes the technical evolution of iframe layout coordination within Google's Blink rendering engine. Traditionally, browsers treat iframes as isolated boxes with a default size of 300x150 pixels, preventing internal content from influencing the parent page's layout. To address this limitation, new CSS and HTML mechanisms like contain-intrinsic-size: from-element are being developed to allow for responsively sized iframes. These experimental features require a mutual opt-in from both the host and the embedded document to ensure security and layout stability. While developers historically relied on complex JavaScript workarounds for resizing, Chromium is moving toward a standardized, browser-driven approach that is currently accessible via experimental flags.