Fix clang style errors in rtp_rtcp and dependant targets

Mark functions with override instead of virtual.
Add explicit non-trivial constructors/assign operators/destructors.
Define them in .cc files instead of inlining
use auto* instead of auto when deduced type is raw pointer

Bug: webrtc:163
Change-Id: I4d8a05d6a64fcc2ca16d02c5fcf9488fda832a6d
Reviewed-on: https://webrtc-review.googlesource.com/48781
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21927}
diff --git a/api/mediastreaminterface.cc b/api/mediastreaminterface.cc
index 0bc5d61..6f08a0c 100644
--- a/api/mediastreaminterface.cc
+++ b/api/mediastreaminterface.cc
@@ -45,4 +45,17 @@
   return new_stats;
 }
 
+VideoTrackInterface::ContentHint VideoTrackInterface::content_hint() const {
+  return ContentHint::kNone;
+}
+
+bool AudioTrackInterface::GetSignalLevel(int* level) {
+  return false;
+}
+
+rtc::scoped_refptr<AudioProcessorInterface>
+AudioTrackInterface::GetAudioProcessor() {
+  return nullptr;
+}
+
 }  // namespace webrtc