chrome: Enforce matching context for new user and incognito profiles

Selecting a new user or incognito profile via Chrome UI may result in
the creation of a new Profile object. If that occurs, we should find
or create a matching CefBrowserContext and CefRequestContext instead
of reusing an existing mismatched context (e.g. using the original
context for an incognito window would be a mismatch). If a new
CefRequestContext will be created the client can now implement
CefBrowserProcessHandler::GetDefaultRequestContextHandler() to
provide the handler for that context.

To test with a new user profile:
1. Click "Profile" icon, select "Add". Now you have 2+ profiles.
2. Click "Profile" icon, select the other user name to create a new
   window using the other user profile.
3. The new window should launch successfully.

To test with a new incognito profile:
1. Select "New Incognito window" from the 3-dot menu.
2. The new window should launch successfully.

To test DevTools window creation for the new profile:
1. Right-click in the new window, select Inspect.
2. The DevTools window should launch successfully.

libcef_dll/ctocpp/browser_process_handler_ctocpp.h

@@ -9,7 +9,7 @@
 // implementations. See the translator.README.txt file in the tools directory
 // for more information.
 //
-// $hash=adc863edb83f2bb42719a92c410289ee338acb0f$
+// $hash=1212f57d4d21fbb85deba5fc02bfe0a38a6d1a04$
 //
 
 #ifndef CEF_LIBCEF_DLL_CTOCPP_BROWSER_PROCESS_HANDLER_CTOCPP_H_
@@ -45,6 +45,8 @@ class CefBrowserProcessHandlerCToCpp
                                    const CefString& current_directory) override;
   void OnScheduleMessagePumpWork(int64_t delay_ms) override;
   CefRefPtr<CefClient> GetDefaultClient() override;
+  CefRefPtr<CefRequestContextHandler> GetDefaultRequestContextHandler()
+      override;
 };
 
 #endif  // CEF_LIBCEF_DLL_CTOCPP_BROWSER_PROCESS_HANDLER_CTOCPP_H_