Enable cpplint for webrtc/examples and fix all uncovered cpplint errors.

BUG=webrtc:5273
TESTED=Fixed issues reported by:
find webrtc/examples/ -type f -name *.cc -o -name *.h | grep -v objc | xargs cpplint.py
followed by 'git cl presubmit'.

NOTRY=True

Review URL: https://codereview.webrtc.org/1504283004

Cr-Commit-Position: refs/heads/master@{#10960}
diff --git a/webrtc/examples/peerconnection/client/peer_connection_client.cc b/webrtc/examples/peerconnection/client/peer_connection_client.cc
index ab6f6ab..9875115 100644
--- a/webrtc/examples/peerconnection/client/peer_connection_client.cc
+++ b/webrtc/examples/peerconnection/client/peer_connection_client.cc
@@ -43,7 +43,7 @@
 #endif
 }
 
-}
+}  // namespace
 
 PeerConnectionClient::PeerConnectionClient()
   : callback_(NULL),