cefclient: Use default window for DevTools non-Views popup (see #3681)

Chrome runtime only supports creation of a Views-hosted DevTools
popup in ChromeBrowserDelegate::CreateDevToolsBrowser if the parent
is also Views-hosted.

To test:
- Run `cefclient --use-native`
- Right click, select "Show DevTools"
- Close both windows and the app should exit

tests/cefclient/browser/root_window_manager.cc

@@ -115,9 +115,13 @@ class ClientRequestContextHandler : public CefRequestContextHandler,
 
 // Ensure a compatible set of window creation attributes.
 void SanityCheckWindowConfig(const bool is_devtools,
-                             bool& use_views,
+                             const bool use_views,
                              bool& use_alloy_style,
                              bool& with_osr) {
+  // This configuration is not supported by cefclient architecture and
+  // should use default window creation instead.
+  CHECK(!(is_devtools && !use_views));
+
   if (MainContext::Get()->UseChromeBootstrap()) {
     if (is_devtools && use_alloy_style) {
       LOG(WARNING)
@@ -125,13 +129,6 @@ void SanityCheckWindowConfig(const bool is_devtools,
              " using Chrome style.";
       use_alloy_style = false;
     }
-
-    if (is_devtools && !use_views) {
-      LOG(WARNING)
-          << "Native parent is not supported with Chrome runtime DevTools;"
-             " using Views.";
-      use_views = true;
-    }
   }
 
   if (!use_alloy_style && with_osr) {
@@ -195,15 +192,15 @@ scoped_refptr<RootWindow> RootWindowManager::CreateRootWindowAsPopup(
     CefBrowserSettings& settings) {
   CEF_REQUIRE_UI_THREAD();
 
-  SanityCheckWindowConfig(is_devtools, use_views, use_alloy_style, with_osr);
-
-  if (MainContext::Get()->UseDefaultPopup()) {
+  if (MainContext::Get()->UseDefaultPopup() || (is_devtools && !use_views)) {
     // Use default window creation for the popup. A new |client| instance is
     // still required by cefclient architecture.
     client = new DefaultClientHandler();
     return nullptr;
   }
 
+  SanityCheckWindowConfig(is_devtools, use_views, use_alloy_style, with_osr);
+
   if (!temp_window_) {
     // TempWindow must be created on the UI thread.
     temp_window_.reset(new TempWindow());