message: Clarify logging docs.
  This change clarifies docs related to
  Cr-Commit-Position: refs/heads/master@{#31680}
diff: @@ -464,9 +464,14 @@ class LogMessage {
  static void SetLogToStderr(bool log_to_stderr);
  // Stream: Any non-blocking stream interface.
  // Installs the |stream| to collect logs with severtiy |min_sev| or higher.
  - // |stream| must live until deinstalled by RemoveLogToStream
  + // |stream| must live until deinstalled by RemoveLogToStream.
  + // If |stream| is the first stream added to the system, we might miss some
  + // early concurrent log statement happening from another thread happening near
  + // this instant.
  static void AddLogToStream(LogSink* stream, LoggingSeverity min_sev);
  - // Removes the specified stream, without destroying it.
  + // Removes the specified stream, without destroying it. When the method
  + // has completed, it's guaranteed that |stream| will receive no more logging
  + // calls.
  static void RemoveLogToStream(LogSink* stream);
  // Returns the severity for the specified stream, of if none is specified,
  // the minimum stream severity.
  @@ -560,7 +565,7 @@ class LogMessage {
  // Holds true with high probability if |streams_| is empty, false with high
  // probability otherwise. Operated on with std::memory_order_relaxed because
  - // it's ok to loose or log some additional statements near the instant streams
  + // it's ok to lose or log some additional statements near the instant streams
  // are added/removed.
  static std::atomic<bool> streams_empty_;
  