Adds new `--show-overlay-browser` command-line flag that creates an
overlay containing an Alloy-style BrowserView. The main BrowserView
may be Chrome- (default) or Alloy-style (add `--use-alloy-style`).
This overlay will only be added to standalone (non-popup) windows.
Popups triggered via the overlay will receive standard Alloy-style
handling in cefclient (e.g. Views-hosted window). Add
`--use-default-popup` for default popup handling.
The client can optionally wait or terminate the render process.
Expose process exit codes via OnRenderProcessTerminated and
CefGetExitCode (fixes#2126).
cefclient: Add a new https://tests/hang page for testing hang behavior.
cefclient: Move message and resource handling to a new BaseClientHandler
class to support loading of test pages in default Chrome UI windows.
