Add exclusive mode option for WASAPI

src/engine/enginebase.h

@@ -129,6 +129,7 @@ class EngineBase : public QObject {
   virtual QString DefaultOutput() = 0;
   virtual bool CustomDeviceSupport(const QString &output) = 0;
   virtual bool ALSADeviceSupport(const QString &output) = 0;
+  virtual bool ExclusiveModeSupport(const QString &output) = 0;
 
   // Plays a media stream represented with the URL 'u' from the given 'beginning' to the given 'end' (usually from 0 to a song's length).
   // Both markers should be passed in nanoseconds. 'end' can be negative, indicating that the real length of 'u' stream is unknown.
@@ -188,6 +189,7 @@ class EngineBase : public QObject {
   void VolumeChanged(const uint volume);
 
  protected:
+  bool exclusive_mode_;
   bool volume_control_;
   uint volume_;
   quint64 beginning_nanosec_;