Adding 'explicit' to these constructors has a low risk of causing compatibility problems: explicit RTCConfiguration(RTCConfigurationType type) explicit IdBase(StatsType type) BUG=webrtc:5267 TESTED=Fixed issues reported by: find webrtc/api -type f -name *.cc -o -name *.h | xargs cpplint.py followed by 'git cl presubmit'. Review-Url: https://codereview.webrtc.org/2663063003 Cr-Commit-Position: refs/heads/master@{#16392}