Enable cpplint for webrtc/modules/pacing and fix all uncovered cpplint errors.

This CL enableds cpplint for webrtc/modules/pacing.

BUG=webrtc:5460
NOTRY=true

TESTED=Fixed issues reported by:
find webrtc/modules/pacing -type f -name *.cc -o -name *.h | xargs cpplint.py
followed by 'git cl presubmit'.

Review URL: https://codereview.webrtc.org/1674423002

Cr-Commit-Position: refs/heads/master@{#11531}

PRESUBMIT.py

@@ -21,6 +21,7 @@ CPPLINT_DIRS = [
   'webrtc/common_video',
   'webrtc/examples',
   'webrtc/modules/bitrate_controller',
+  'webrtc/modules/pacing',
   'webrtc/modules/remote_bitrate_estimator',
   'webrtc/modules/rtp_rtcp',
   'webrtc/modules/video_coding',