Reland "Enable the clang style plugin in rtc_base/"

This is a reland of Id63f0deb7b335690157ab157c35177b7836688da.

Original change's description:
> 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}

Bug: webrtc:163
Change-Id: I861a5fe741215115b0e7a2be9c0786836ff5376e
Reviewed-on: https://webrtc-review.googlesource.com/15040
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20416}
diff --git a/rtc_base/sslstreamadapter_unittest.cc b/rtc_base/sslstreamadapter_unittest.cc
index 03aabd8..3999ac5 100644
--- a/rtc_base/sslstreamadapter_unittest.cc
+++ b/rtc_base/sslstreamadapter_unittest.cc
@@ -241,7 +241,7 @@
     rtc::SetRandomTestMode(true);
   }
 
-  ~SSLStreamAdapterTestBase() {
+  ~SSLStreamAdapterTestBase() override {
     // Put it back for the next test.
     rtc::SetRandomTestMode(false);
   }