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/defaults.h b/webrtc/examples/peerconnection/client/defaults.h
index 7b50397..f4d3bf5 100644
--- a/webrtc/examples/peerconnection/client/defaults.h
+++ b/webrtc/examples/peerconnection/client/defaults.h
@@ -8,8 +8,8 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef PEERCONNECTION_SAMPLES_CLIENT_DEFAULTS_H_
-#define PEERCONNECTION_SAMPLES_CLIENT_DEFAULTS_H_
+#ifndef WEBRTC_EXAMPLES_PEERCONNECTION_CLIENT_DEFAULTS_H_
+#define WEBRTC_EXAMPLES_PEERCONNECTION_CLIENT_DEFAULTS_H_
 #pragma once
 
 #include <string>
@@ -27,4 +27,4 @@
 std::string GetDefaultServerName();
 std::string GetPeerName();
 
-#endif  // PEERCONNECTION_SAMPLES_CLIENT_DEFAULTS_H_
+#endif  // WEBRTC_EXAMPLES_PEERCONNECTION_CLIENT_DEFAULTS_H_