Valid json optimization

Added ~20% performance boost be removing extra allocation when
Valid() is called with a json string.

gjson.go

@@ -2038,7 +2038,7 @@ func validnull(data []byte, i int) (outi int, ok bool) {
 //  value := gjson.Get(json, "name.last")
 //
 func Valid(json string) bool {
-	_, ok := validpayload([]byte(json), 0)
+	_, ok := validpayload(stringBytes(json), 0)
 	return ok
 }
 

gjson_gae.go

@@ -8,3 +8,7 @@ func getBytes(json []byte, path string) Result {
 func fillIndex(json string, c *parseContext) {
 	// noop. Use zero for the Index value.
 }
+
+func stringBytes(s string) []byte {
+	return []byte(s)
+}

gjson_ngae.go

@@ -67,3 +67,11 @@ func fillIndex(json string, c *parseContext) {
 		}
 	}
 }
+
+func stringBytes(s string) []byte {
+	return *(*[]byte)(unsafe.Pointer(&reflect.SliceHeader{
+		Data: (*reflect.StringHeader)(unsafe.Pointer(&s)).Data,
+		Len:  len(s),
+		Cap:  len(s),
+	}))
+}

gjson_test.go

@@ -1431,3 +1431,23 @@ func TestArrayValues(t *testing.T) {
 	}
 
 }
+
+func BenchmarkValid(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Valid(complicatedJSON)
+	}
+}
+
+func BenchmarkValidBytes(b *testing.B) {
+	complicatedJSON := []byte(complicatedJSON)
+	for i := 0; i < b.N; i++ {
+		ValidBytes(complicatedJSON)
+	}
+}
+
+func BenchmarkGoStdlibValidBytes(b *testing.B) {
+	complicatedJSON := []byte(complicatedJSON)
+	for i := 0; i < b.N; i++ {
+		json.Valid(complicatedJSON)
+	}
+}