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..e4fc45c13bba640d9e5148420aa5e63802e7c1b0 100644
--- a/perf/go/parser/parser_test.go
+++ b/perf/go/parser/parser_test.go
@@ -131,6 +131,20 @@ func TestAve(t *testing.T) {
 	}
 }
 
+func TestRatio(t *testing.T) {
+	ctx := newTestContext()
+	ctx.Tile.Traces["t1"].(*types.PerfTrace).Values = []float64{10, 4, 100, 50}
+	ctx.Tile.Traces["t2"].(*types.PerfTrace).Values = []float64{5, 2, 4, 5}
+
+	traces, err := ctx.Eval(`ratio(
+                ave(fill(filter("source_type=skp&config=gpu&bench_type=playback"))),

[jcgregorio, 2014/10/17 11:43:55]

ave(fill(filter("config=gpu"))),

[tfarina, 2014/10/17 21:14:23]

Done.

+                ave(fill(filter("source_type=skp&config=8888&bench_type=playback")))

[jcgregorio, 2014/10/17 11:43:55]

ave(fill(filter("config=8888"))),

[tfarina, 2014/10/17 21:14:23]

Done.

+        )`)
+	if err != nil {
+		t.Fatalf("Failed to eval ratio() test: %s", err)
+	}
+}
+
 func TestFill(t *testing.T) {
 	ctx := newTestContext()
 	ctx.Tile.Traces["t1"].(*types.PerfTrace).Values = []float64{1e100, 1e100, 2, 3, 1e100, 5}