These errors are reported when compiling Cronet.

../../components/cronet/android/java/src/org/chromium/net/impl/CronetMetrics.java:209: warning: [MissingOverride] getTtfbMs implements method in Metrics; expected @Override
    public Long getTtfbMs() {
                ^
    (see http://errorprone.info/bugpattern/MissingOverride)
  Did you mean '@Override @Nullable'?
../../components/cronet/android/java/src/org/chromium/net/impl/CronetMetrics.java:214: warning: [MissingOverride] getTotalTimeMs implements method in Metrics; expected @Override
    public Long getTotalTimeMs() {
                ^
    (see http://errorprone.info/bugpattern/MissingOverride)
  Did you mean '@Override @Nullable'?
../../components/cronet/android/java/src/org/chromium/net/impl/CronetMetrics.java:219: warning: [MissingOverride] getSentByteCount implements method in Metrics; expected @Override
    public Long getSentByteCount() {
                ^
    (see http://errorprone.info/bugpattern/MissingOverride)
  Did you mean '@Override @Nullable'?
../../components/cronet/android/java/src/org/chromium/net/impl/CronetMetrics.java:224: warning: [MissingOverride] getReceivedByteCount implements method in Metrics; expected @Override
    public Long getReceivedByteCount() {