Convert 'Testable' interface into an optional filter.

go/src/infra/gae/libs/gae/filters/featureBreaker/gi.go

Index: go/src/infra/gae/libs/gae/filters/featureBreaker/gi.go
diff --git a/go/src/infra/gae/libs/gae/filters/featureBreaker/gi.go b/go/src/infra/gae/libs/gae/filters/featureBreaker/gi.go
new file mode 100644
index 0000000000000000000000000000000000000000..feaa003d478cd9552216ee04df458c2e83403161
--- /dev/null
+++ b/go/src/infra/gae/libs/gae/filters/featureBreaker/gi.go
@@ -0,0 +1,74 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package featureBreaker
+
+import (
+	"golang.org/x/net/context"
+	"time"
+
+	"infra/gae/libs/gae"
+)
+
+type giState struct {
+	*state
+
+	gae.GlobalInfo
+}
+
+func (g *giState) ModuleHostname(module, version, instance string) (ret string, err error) {
+	err = g.run(func() (err error) {
+		ret, err = g.GlobalInfo.ModuleHostname(module, version, instance)
+		return
+	})
+	return
+}
+
+func (g *giState) ServiceAccount() (ret string, err error) {
+	err = g.run(func() (err error) {
+		ret, err = g.GlobalInfo.ServiceAccount()
+		return
+	})
+	return
+}
+
+func (g *giState) Namespace(namespace string) (ret context.Context, err error) {
+	err = g.run(func() (err error) {
+		ret, err = g.GlobalInfo.Namespace(namespace)
+		return
+	})
+	return
+}
+
+func (g *giState) AccessToken(scopes ...string) (token string, expiry time.Time, err error) {
+	err = g.run(func() (err error) {
+		token, expiry, err = g.GlobalInfo.AccessToken(scopes...)
+		return
+	})
+	return
+}
+
+func (g *giState) PublicCertificates() (ret []gae.GICertificate, err error) {
+	err = g.run(func() (err error) {
+		ret, err = g.GlobalInfo.PublicCertificates()
+		return
+	})
+	return
+}
+
+func (g *giState) SignBytes(bytes []byte) (keyName string, signature []byte, err error) {
+	err = g.run(func() (err error) {
+		keyName, signature, err = g.GlobalInfo.SignBytes(bytes)
+		return
+	})
+	return
+}
+
+// FilterGI installs a counter GlobalInfo filter in the context.
+func FilterGI(c context.Context, defaultError error) (context.Context, FeatureBreaker) {
+	state := newState(defaultError)
+	return gae.AddGIFilters(c, func(ic context.Context, gi gae.GlobalInfo) gae.GlobalInfo {
+		return &giState{state, gi}
+	}), state
+}