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/socketstream.h

@@ -22,22 +22,26 @@ namespace rtc {
 class SocketStream : public StreamInterface, public sigslot::has_slots<> {
  public:
   explicit SocketStream(AsyncSocket* socket);
-  virtual ~SocketStream();
+  ~SocketStream() override;
 
   void Attach(AsyncSocket* socket);
   AsyncSocket* Detach();
 
   AsyncSocket* GetSocket() { return socket_; }
 
-  virtual StreamState GetState() const;
+  StreamState GetState() const override;
 
-  virtual StreamResult Read(void* buffer, size_t buffer_len,
-                            size_t* read, int* error);
+  StreamResult Read(void* buffer,
+                    size_t buffer_len,
+                    size_t* read,
+                    int* error) override;
 
-  virtual StreamResult Write(const void* data, size_t data_len,
-                             size_t* written, int* error);
+  StreamResult Write(const void* data,
+                     size_t data_len,
+                     size_t* written,
+                     int* error) override;
 
-  virtual void Close();
+  void Close() override;
 
  private:
   void OnConnectEvent(AsyncSocket* socket);