message: Fix member shadowing causing buckconfigs with -Werror=shadow to fail
  Summary: This was causing targets such as //hphp/tools/tc-print to fail due to Buckconfigs with set `-Werror=shadow`. Struct members of `HistogramSpec` are now underscore suffixed.
diff: @@ -394,13 +394,13 @@ struct HistogramSpec {
  template <typename... Args>
  HistogramSpec(
  - int64_t bucketWidth,
  - int64_t min,
  - int64_t max,
  + int64_t bucketWidth_,
  + int64_t min_,
  + int64_t max_,
  const Args&... args)
  - : bucketWidth(bucketWidth),
  - min(min),
  - max(max),
  + : bucketWidth(bucketWidth_),
  + min(min_),
  + max(max_),
  levels(MinuteTenMinuteHourTimeSeries<CounterType>()) {
  ctorHandleArgs(args...);
  }
  @@ -426,8 +426,8 @@ struct HistogramSpec {
  this->percentiles.push_back(pctile);
  }
  - void ctorHandleArg(const MultiLevelTimeSeries<CounterType>& _levels) {
  - this->levels = _levels;
  + void ctorHandleArg(const MultiLevelTimeSeries<CounterType>& levels_) {
  + this->levels = levels_;
  }
  template <typename... Args>
  