Apple is building a web browser engine, Google is building a sandboxed application runtime - that happens to be a web browser engine superset.
Google is building a web browser engine that matches the current needs of developers, while Apple has under-invested in its engine for years, leaving it rigged with bugs and lagging behind others in an obvious attempt to prevents web apps from competing with natives apps on iOS to preserve its App Store revenues and enrich its app ecosystem to boost iDevices sales.