Prevent calling internal metrics code with invalid values.

base/metrics/histogram.h

Index: base/metrics/histogram.h
diff --git a/base/metrics/histogram.h b/base/metrics/histogram.h
index 0b946136b0fb7d9046346d1914c6a66e3eb0f094..f437ffce70859b053d1d0bab58a5396fc238d563 100644
--- a/base/metrics/histogram.h
+++ b/base/metrics/histogram.h
@@ -430,8 +430,14 @@ class BASE_EXPORT Histogram {
   };
 
   //----------------------------------------------------------------------------
-  // minimum should start from 1. 0 is invalid as a minimum. 0 is an implicit
-  // default underflow bucket.
+  // For a valid histogram, input should follow these restrictions:
+  // minimum > 0

[jar (doing other things), 2012/01/05 17:35:14]

There is fixup code in histograms for this, so minimum can be smaller... but it
is implicitly fixed up to 1. I'd suggest changing line 434 to read:

// if minimum is not positive, it is implicitly replaced by 1.

[rkc, 2012/01/06 00:08:01]

Done.

+  // maximum > minimum
+  // buckets > 2 [minimum buckets needed: underflow, overflow and the range]
+  // Additionally,
+  // buckets <= (maximum - minimum + 2) - this is to ensure that we don't have
+  // more buckets than the range of numbers; having more buckets than 1 per
+  // value in the range would be nonsensical.
   static Histogram* FactoryGet(const std::string& name,
                                Sample minimum,
                                Sample maximum,