Called when a browser has recieved a request to close. This may result directly from a call to CefBrowserHost::CloseBrowser() or indirectly if the browser is a top-level OS window created by CEF and the user attempts to close the window. This method will be called after the JavaScript 'onunload' event has been fired. It will not be called for browsers after the associated OS window has been destroyed (for those browsers it is no longer possible to cancel the close). If CEF created an OS window for the browser returning false will send an OS close notification to the browser window's top-level owner (e.g. WM_CLOSE on Windows, performClose: on OS-X and "delete_event" on Linux). If no OS window exists (window rendering disabled) returning false will cause the browser object to be destroyed immediately. Return true if the browser is parented to another window and that other window needs to receive close notification via some non-standard technique. If an application provides its own top-level window it should handle OS close notifications by calling CefBrowserHost::CloseBrowser(false) instead of immediately closing (see the example below). This gives CEF an opportunity to process the 'onbeforeunload' event and optionally cancel the close before DoClose() is called. The CefLifeSpanHandler::OnBeforeClose() method will be called immediately before the browser object is destroyed. The application should only exit after OnBeforeClose() has been called for all existing browsers. If the browser represents a modal window and a custom modal loop implementation was provided in CefLifeSpanHandler::RunModal() this callback should be used to restore the opener window to a usable state. By way of example consider what should happen during window close when the browser is parented to an application-provided top-level OS window. 1. User clicks the window close button which sends an OS close notification (e.g. WM_CLOSE on Windows, performClose: on OS-X and "delete_event" on Linux). 2. Application's top-level window receives the close notification and: A. Calls CefBrowserHost::CloseBrowser(false). B. Cancels the window close. 3. JavaScript 'onbeforeunload' handler executes and shows the close confirmation dialog (which can be overridden via CefJSDialogHandler::OnBeforeUnloadDialog()). 4. User approves the close. 5. JavaScript 'onunload' handler executes. 6. Application's DoClose() handler is called. Application will: A. Set a flag to indicate that the next close attempt will be allowed. B. Return false. 7. CEF sends an OS close notification. 8. Application's top-level window receives the OS close notification and allows the window to close based on the flag from #6B. 9. Browser OS window is destroyed. 10. Application's CefLifeSpanHandler::OnBeforeClose() handler is called and the browser object is destroyed. 11. Application exits by calling CefQuitMessageLoop() if no other browsers exist.

protected virtual bool DoClose(
	CefBrowser browser
)

protected virtual bool DoClose(
	CefBrowser browser
)