Fix clang style warnings in webrtc/base

Mostly this consists of marking functions with override when
applicable, and moving function bodies from .h to .cc files.

Not inlining virtual functions with simple bodies such as

  { return false; }

strikes me as probably losing more in readability than we gain in
binary size and compilation time, but I guess it's just like any other
case where enabling a generally good warning forces us to write
slightly worse code in a couple of places.

BUG=163
R=kjellander@webrtc.org, tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/47429004

Cr-Commit-Position: refs/heads/master@{#8656}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8656 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/base/transformadapter.h

@@ -45,20 +45,24 @@ public:
   TransformAdapter(StreamInterface * stream,
                    TransformInterface * transform,
                    bool direction_read);
-  virtual ~TransformAdapter();
-  
-  virtual StreamResult Read(void * buffer, size_t buffer_len,
-                            size_t * read, int * error);
-  virtual StreamResult Write(const void * data, size_t data_len,
-                             size_t * written, int * error);
-  virtual void Close();
+  ~TransformAdapter() override;
+
+  StreamResult Read(void* buffer,
+                    size_t buffer_len,
+                    size_t* read,
+                    int* error) override;
+  StreamResult Write(const void* data,
+                     size_t data_len,
+                     size_t* written,
+                     int* error) override;
+  void Close() override;
 
   // Apriori, we can't tell what the transformation does to the stream length.
-  virtual bool GetAvailable(size_t* size) const { return false; }
-  virtual bool ReserveSize(size_t size) { return true; }
+  bool GetAvailable(size_t* size) const override;
+  bool ReserveSize(size_t size) override;
 
   // Transformations might not be restartable
-  virtual bool Rewind() { return false; }
+  virtual bool Rewind();
 
 private:
   enum State { ST_PROCESSING, ST_FLUSHING, ST_COMPLETE, ST_ERROR };