Wait for CefBrowserContext initialization (see issue #2969)

With the Chrome runtime, Profile initialization may be asynchronous. Code that
waited on CefBrowserContext creation now needs to wait on CefBrowserContext
initialization instead.

libcef/browser/browser_host_base.h

@@ -65,7 +65,7 @@ struct CefBrowserCreateParams {
 
   // Initial URL to load. May be empty. If this is a valid extension URL then
   // the browser will be created as an app view extension host.
-  GURL url;
+  CefString url;
 
   // Browser settings.
   CefBrowserSettings settings;