Add ratio calculation to take the ratio of two calculations.

perf/go/parser/parser_test.go

 package parser
 
 import (
         "math"
         "testing"
 
         "skia.googlesource.com/buildbot.git/perf/go/config"
         "skia.googlesource.com/buildbot.git/perf/go/types"
 )
 
@@ skipping 113 matching lines @@
                 t.Errorf("ave() returned wrong length: Got %v Want %v", got, want)
         }
 
         for i, want := range []float64{1.0, 0.5, -2.0, 1e100} {
                 if got := traces[0].Values[i]; !near(got, want) {
                         t.Errorf("Distance mismatch: Got %v Want %v", got, want)
                 }
         }
 }
 
+func TestRatio(t *testing.T) {
+        ctx := newTestContext()
+}
+
 func TestFill(t *testing.T) {
         ctx := newTestContext()
         ctx.Tile.Traces["t1"].(*types.PerfTrace).Values = []float64{1e100, 1e100, 2, 3, 1e100, 5}
         delete(ctx.Tile.Traces, "t2")
         traces, err := ctx.Eval(`fill(filter("config=8888"))`)
         if err != nil {
                 t.Fatalf("Failed to eval fill() test: %s", err)
         }
         if got, want := len(traces), 1; got != want {
                 t.Errorf("fill() returned wrong length: Got %v Want %v", got, want)
         }
 
         for i, want := range []float64{2, 2, 2, 3, 3, 5} {
                 if got := traces[0].Values[i]; !near(got, want) {
                         t.Errorf("Distance mismatch: Got %v Want %v", got, want)
                 }
         }
 }