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
diff --git a/webrtc/base/asyncpacketsocket.h b/webrtc/base/asyncpacketsocket.h
index dd91ea1..8054155 100644
--- a/webrtc/base/asyncpacketsocket.h
+++ b/webrtc/base/asyncpacketsocket.h
@@ -22,10 +22,8 @@
 // extension, including the information needed to update the authentication tag
 // after changing the value.
 struct PacketTimeUpdateParams {
-  PacketTimeUpdateParams()
-      : rtp_sendtime_extension_id(-1), srtp_auth_tag_len(-1),
-        srtp_packet_index(-1) {
-  }
+  PacketTimeUpdateParams();
+  ~PacketTimeUpdateParams();
 
   int rtp_sendtime_extension_id;    // extension header id present in packet.
   std::vector<char> srtp_auth_key;  // Authentication key.
@@ -75,8 +73,8 @@
     STATE_CONNECTED
   };
 
-  AsyncPacketSocket() { }
-  virtual ~AsyncPacketSocket() { }
+  AsyncPacketSocket();
+  ~AsyncPacketSocket() override;
 
   // Returns current local address. Address may be set to NULL if the
   // socket is not bound yet (GetState() returns STATE_BINDING).