nanobench: add median and --cpu/--gpu

tools/Stats.h

 #ifndef Stats_DEFINED
 #define Stats_DEFINED
 
+#include "SkTSort.h"
+
 struct Stats {
     Stats(const double samples[], int n) {
         min = samples[0];
         max = samples[0];
         for (int i = 0; i < n; i++) {
             if (samples[i] < min) { min = samples[i]; }
             if (samples[i] > max) { max = samples[i]; }
         }
 
         double sum = 0.0;
         for (int i = 0 ; i < n; i++) {
             sum += samples[i];
         }
         mean = sum / n;
 
         double err = 0.0;
         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];
     }
 
     double min;
     double max;
     double mean;  // Estimate of population mean.
     double var;   // Estimate of population variance.
+    double median;
 };
 
 #endif//Stats_DEFINED