fix include dependencies in folly/stats

Summary:
Histogram-defs.h depends on Histogram.h, so it should include it.

This missing dependency is especially annoying because users who
include both Histogram.h and Histogram-defs.h will find that
clang-format reorders the includes such that Histogram-defs.h will
be included before Histogram.h, which breaks the build.

Same for BucketedTimeSeries-defs.h and TimeseriesHistogram-defs.h.

Reviewed By: pixelb

Differential Revision: D4366282

fbshipit-source-id: 518ef315154c28beb091e5c097db2bec6eea3ba0

folly/stats/BucketedTimeSeries-defs.h

@@ -19,6 +19,7 @@
 #include <algorithm>
 #include <glog/logging.h>
 #include <folly/Likely.h>
+#include <folly/stats/BucketedTimeSeries.h>
 
 namespace folly {
 

folly/stats/Histogram-defs.h

@@ -17,6 +17,7 @@
 #pragma once
 
 #include <folly/Conv.h>
+#include <folly/stats/Histogram.h>
 
 #include <glog/logging.h>
 

folly/stats/TimeseriesHistogram-defs.h

@@ -17,9 +17,10 @@
 #pragma once
 
 #include <folly/Conv.h>
+#include <folly/stats/BucketedTimeSeries-defs.h>
 #include <folly/stats/Histogram-defs.h>
 #include <folly/stats/MultiLevelTimeSeries-defs.h>
-#include <folly/stats/BucketedTimeSeries-defs.h>
+#include <folly/stats/TimeseriesHistogram.h>
 
 namespace folly {