FBTF: Fix more ctor/dtors found by clang plugin.

media/base/filters.h

Index: media/base/filters.h
diff --git a/media/base/filters.h b/media/base/filters.h
index 65a33ee65e66f1dd21659d60996df97959032e59..d9edfc1f6d82ec3be4f865fdb0dae97df83b4caf 100644
--- a/media/base/filters.h
+++ b/media/base/filters.h
@@ -270,6 +270,9 @@ class VideoDecoder : public MediaFilter {
     consume_video_frame_callback_->Run(frame);
   }
 
+  VideoDecoder();
+  virtual ~VideoDecoder();
+
  private:
   scoped_ptr<ConsumeVideoFrameCallback> consume_video_frame_callback_;
 };
@@ -309,6 +312,10 @@ class AudioDecoder : public MediaFilter {
   // We could also pass empty pointer here to let decoder provide buffers pool.
   virtual void ProduceAudioSamples(scoped_refptr<Buffer> buffer) = 0;
 
+ protected:
+  AudioDecoder();
+  ~AudioDecoder();
+
  private:
   scoped_ptr<ConsumeAudioSamplesCallback> consume_audio_samples_callback_;
 };