Adds role-aware collapsing of off-screen nodes to CDP accessibility tree
serialization (Accessibility.getFullAXTree). When enabled, off-screen
landmarks and headings are serialized as summaries (role + name only)
and other off-screen nodes are pruned. Position:fixed/sticky descendants
of off-screen parents are still discovered and fully serialized.
Reduces snapshot size for AI agents using Playwright ariaSnapshot().
Platform screen readers are unaffected — they use a separate code path.
CDP nodesUpdated events are suppressed when active.
The setting is a per-browser CefBrowserSettings field threaded through
WebPreferences, with a runtime override via SetAxViewportCollapse().
Both APIs are guarded with CEF_API_ADDED(CEF_EXPERIMENTAL).
Marshall Greenblatt
c5b2ec2b1f