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/PRESUBMIT.py b/PRESUBMIT.py
index be26269..9747d91 100755
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -18,6 +18,7 @@
 CPPLINT_DIRS = [
   'webrtc/audio',
   'webrtc/call',
+  'webrtc/examples',
   'webrtc/modules/video_processing',
   'webrtc/video',
 ]