Enable the clang style plugin in rtc_base/

Enabled the plugin and cleaned up all issues it found.

Bug: webrtc:163
Change-Id: Id63f0deb7b335690157ab157c35177b7836688da
Reviewed-on: https://webrtc-review.googlesource.com/14660
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20401}

rtc_base/messagequeue_unittest.cc

@@ -101,10 +101,9 @@ TEST_F(MessageQueueTest, DisposeNotLocked) {
 class DeletedMessageHandler : public MessageHandler {
  public:
   explicit DeletedMessageHandler(bool* deleted) : deleted_(deleted) { }
-  ~DeletedMessageHandler() {
-    *deleted_ = true;
-  }
-  void OnMessage(Message* msg) { }
+  ~DeletedMessageHandler() override { *deleted_ = true; }
+  void OnMessage(Message* msg) override {}
+
  private:
   bool* deleted_;
 };