Fix chromium-style warnings in webrtc/sound/.

webrtc/sound/soundoutputstreaminterface.h

Index: webrtc/sound/soundoutputstreaminterface.h
diff --git a/webrtc/sound/soundoutputstreaminterface.h b/webrtc/sound/soundoutputstreaminterface.h
index f56d39b7c90c151c0d905b1c2af0d77245a3115c..a94147b838469cdce2ec239896daf25cbcfdc4e4 100644
--- a/webrtc/sound/soundoutputstreaminterface.h
+++ b/webrtc/sound/soundoutputstreaminterface.h
@@ -21,7 +21,7 @@ namespace rtc {
 // DisableBufferMonitoring() are the same as for rtc::Worker.
 class SoundOutputStreamInterface {
  public:
-  virtual ~SoundOutputStreamInterface() {}
+  virtual ~SoundOutputStreamInterface();
 
   // Enables monitoring the available buffer space on the current thread.
   virtual bool EnableBufferMonitoring() = 0;
@@ -61,7 +61,7 @@ class SoundOutputStreamInterface {
   sigslot::signal2<size_t, SoundOutputStreamInterface *> SignalBufferSpace;
 
  protected:
-  SoundOutputStreamInterface() {}
+  SoundOutputStreamInterface();
 
  private:
   RTC_DISALLOW_COPY_AND_ASSIGN(SoundOutputStreamInterface);