s2: Add -benchmark_brute_force flag to aid in testing.

Updates #59.

Signed-off-by: David Symonds <dsymonds@golang.org>

Author: rsned

s2/s2_test.go

@@ -15,6 +15,7 @@
 package s2
 
 import (
+	"flag"
 	"io"
 	"math"
 	"math/rand"
@@ -25,6 +26,12 @@ import (
 	"github.com/golang/geo/s1"
 )
 
+var (
+	// To set in testing add "--benchmark_brute_force=true" to your test command.
+	benchmarkBruteForce = flag.Bool("benchmark_brute_force", false,
+		"When set, use brute force algorithms in benchmarking.")
+)
+
 // float64Eq reports whether the two values are within the default epsilon.
 func float64Eq(x, y float64) bool { return float64Near(x, y, epsilon) }