Fix dangling raw_ptr errors and related issues (see #3239)

- Use raw_ptr in class container fields.
- Use defined lifespan for StreamReaderURLLoader.
- Fix lifespan assumptions for WebContents/RFH usage.

libcef/browser/chrome/chrome_browser_host_impl.h

@@ -177,6 +177,7 @@ class ChromeBrowserHostImpl : public CefBrowserHostBase {
 
   raw_ptr<Browser> browser_ = nullptr;
   CefWindowHandle host_window_handle_ = kNullWindowHandle;
+  bool is_destroying_browser_ = false;
 
   base::WeakPtrFactory<ChromeBrowserHostImpl> weak_ptr_factory_{this};
 };