Add ratio calculation to take the ratio of two calculations.

perf/go/parser/parser_test.go

Index: perf/go/parser/parser_test.go
diff --git a/perf/go/parser/parser_test.go b/perf/go/parser/parser_test.go
index 71fbebf5790e8fea8292a02584a59d684212c3ad..9f3a62c82a02393a1757baee1ea901b5ad572f6c 100644
--- a/perf/go/parser/parser_test.go
+++ b/perf/go/parser/parser_test.go
@@ -131,6 +131,12 @@ func TestAve(t *testing.T) {
 	}
 }
 
+func TestRatio(t *testing.T) {
+	ctx := newTestContext()
+	ctx.Tile.Traces["t1"].(*types.PerfTrace).Values = []float64{1.0, -1.0, 1e100, 1e100}

[tfarina, 2014/10/16 17:42:30]

I think I can have more reasonable numbers in these slices. For easier
computation.

+	ctx.Tile.Traces["t2"].(*types.PerfTrace).Values = []float64{1e100, 2.0, -2.0, 1e100}
+}

[tfarina, 2014/10/16 17:42:30]

Then have:

traces, err := ctx.Eval(`ratio( 
ave(fill(filter("source_type=skp&config=gpu&bench_type=playback"))),
ave(fill(filter("source_type=skp&config=8888&bench_type=playback")))
)`)

+
 func TestFill(t *testing.T) {
 	ctx := newTestContext()
 	ctx.Tile.Traces["t1"].(*types.PerfTrace).Values = []float64{1e100, 1e100, 2, 3, 1e100, 5}