Disallow non-sparse histograms with too many buckets.

base/metrics/histogram.cc

Index: base/metrics/histogram.cc
diff --git a/base/metrics/histogram.cc b/base/metrics/histogram.cc
index 09f0bbb67131e84417f8493971f52aa6603b06af..1f6a955f86637ae0942e248dbb791179d305e7e7 100644
--- a/base/metrics/histogram.cc
+++ b/base/metrics/histogram.cc
@@ -400,6 +400,13 @@ bool Histogram::InspectConstructionArguments(const std::string& name,
     check_okay = false;
     *bucket_count = 3;
   }
+  // Very high bucket counts are wasteful. Use a sparse histogram instead.
+  // Value of 10002 equals a user-supplied value of 10k + 2 overflow buckets.
+  constexpr uint32_t kMaxBucketCount = 10002;

[bcwhite, 2017/05/25 19:21:41]

Even 10k sounds really, really large.

[Alexei Svitkine (slow), 2017/05/25 19:24:04]

Yeah agreed. There was a unit test that was using 10k so I picked a limit that
doesn't require other changes for now. We can reduce it later - in code reviews
I usually push back on anything 100 in size or more when I see it. :)

+  if (*bucket_count > kMaxBucketCount) {
+    check_okay = false;
+    *bucket_count = kMaxBucketCount;
+  }
   if (*bucket_count > static_cast<uint32_t>(*maximum - *minimum + 2)) {
     check_okay = false;
     *bucket_count = static_cast<uint32_t>(*maximum - *minimum + 2);