chrome: Use default Browser creation for picture-in-picture popups (see issue #3448)

Note: In current master (based on M111), document PiP partially works when
run with the `--enable-features=DocumentPictureInPictureAPI` command-line
flag. However, the document PiP implementation at this Chromium version is
missing fixes that have already been cherry-picked to the 5563 release
branch. Those fixes will only be available in master after the next Chromium
update (to M112).

tests/cefclient/browser/client_handler.cc

@@ -767,6 +767,12 @@ bool ClientHandler::OnBeforePopup(
     bool* no_javascript_access) {
   CEF_REQUIRE_UI_THREAD();
 
+  if (target_disposition == WOD_NEW_PICTURE_IN_PICTURE) {
+    // Use default handling for document picture-in-picture popups.
+    client = nullptr;
+    return false;
+  }
+
   // Return true to cancel the popup window.
   return !CreatePopupWindow(browser, false, popupFeatures, windowInfo, client,
                             settings);