Add main document launch support

Main document is an invisble document, so the Runtime class is modified to
support create a Runtime without native app window. The
Runtime::CreateWithDefaultWindow() static function now works like the previous
Runtime::Create() function.

So different from local path launch, the main document launch will use
Runtime::Create() to create an invisible runtime. Currently we support both
launch from main document and local path, however the local path launch support
may be deprecated in the future.
Add main document browser test