nanobench: add --runOnce.

tools/Stats.h

 #ifndef Stats_DEFINED
 #define Stats_DEFINED
 
 #include <math.h>
 
 #include "SkString.h"
 #include "SkTSort.h"
 
 static const char* kBars[] = { "▁", "▂", "▃", "▄", "▅", "▆", "▇", "█" };
 
@@ skipping 16 matching lines @@
         for (int i = 0 ; i < n; i++) {
             err += (samples[i] - mean) * (samples[i] - mean);
         }
         var = err / (n-1);
 
         SkAutoTMalloc<double> sorted(n);
         memcpy(sorted.get(), samples, n * sizeof(double));
         SkTQSort(sorted.get(), sorted.get() + n - 1);
         median = sorted[n/2];
 
+        // Normalize samples to [min, max] in as many quanta as we have distinct bars to print.
         for (int i = 0; i < n; i++) {
+            if (min == max) {
+                // All samples are the same value.  Don't divide by zero.
+                plot.append(kBars[0]);
+                continue;
+            }
+
             double s = samples[i];
-            // Normalize samples to [min, max] in as many quanta as we have distinct bars to print.
             s -= min;
             s /= (max - min);
             s *= (SK_ARRAY_COUNT(kBars) - 1);
             const size_t bar = (size_t)round(s);
             SK_ALWAYSBREAK(bar < SK_ARRAY_COUNT(kBars));
             plot.append(kBars[bar]);
         }
     }
 
     double min;
     double max;
     double mean;    // Estimate of population mean.
     double var;     // Estimate of population variance.
     double median;
     SkString plot;  // A single-line bar chart (_not_ histogram) of the samples.
 };
 
 #endif//Stats_DEFINED