Remove DISALLOW_ macro from libcef/ (see issue #3234)

Also perform related C++ cleanup:
- Use =default instead of {} for default implementations of
  constructors/destructors.
- Replace typedef with using.

libcef/browser/audio_loopback_stream_creator.h

@@ -6,7 +6,6 @@
 #define CEF_LIBCEF_BROWSER_AUDIO_LOOPBACK_STREAM_CREATOR_H_
 
 #include "base/callback.h"
-#include "base/macros.h"
 #include "content/browser/media/forwarding_audio_stream_factory.h"
 #include "content/common/content_export.h"
 #include "media/mojo/mojom/audio_data_pipe.mojom.h"
@@ -25,6 +24,11 @@ class AudioParameters;
 class CefAudioLoopbackStreamCreator final {
  public:
   CefAudioLoopbackStreamCreator();
+
+  CefAudioLoopbackStreamCreator(const CefAudioLoopbackStreamCreator&) = delete;
+  CefAudioLoopbackStreamCreator& operator=(
+      const CefAudioLoopbackStreamCreator&) = delete;
+
   ~CefAudioLoopbackStreamCreator();
 
   // The callback that is called when the requested stream is created.
@@ -44,8 +48,6 @@ class CefAudioLoopbackStreamCreator final {
 
  private:
   content::ForwardingAudioStreamFactory factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(CefAudioLoopbackStreamCreator);
 };
 
 #endif  // CEF_LIBCEF_BROWSER_AUDIO_LOOPBACK_STREAM_CREATOR_H_