diff --git a/vendor/google.golang.org/appengine/internal/api_common.go b/vendor/google.golang.org/appengine/internal/api_common.go
new file mode 100644
index 0000000..e0c0b21
--- /dev/null
+++ b/vendor/google.golang.org/appengine/internal/api_common.go
@@ -0,0 +1,123 @@
+// Copyright 2015 Google Inc. All rights reserved.
+// Use of this source code is governed by the Apache 2.0
+// license that can be found in the LICENSE file.
+
+package internal
+
+import (
+	"errors"
+	"os"
+
+	"github.com/golang/protobuf/proto"
+	netcontext "golang.org/x/net/context"
+)
+
+var errNotAppEngineContext = errors.New("not an App Engine context")
+
+type CallOverrideFunc func(ctx netcontext.Context, service, method string, in, out proto.Message) error
+
+var callOverrideKey = "holds []CallOverrideFunc"
+
+func WithCallOverride(ctx netcontext.Context, f CallOverrideFunc) netcontext.Context {
+	// We avoid appending to any existing call override
+	// so we don't risk overwriting a popped stack below.
+	var cofs []CallOverrideFunc
+	if uf, ok := ctx.Value(&callOverrideKey).([]CallOverrideFunc); ok {
+		cofs = append(cofs, uf...)
+	}
+	cofs = append(cofs, f)
+	return netcontext.WithValue(ctx, &callOverrideKey, cofs)
+}
+
+func callOverrideFromContext(ctx netcontext.Context) (CallOverrideFunc, netcontext.Context, bool) {
+	cofs, _ := ctx.Value(&callOverrideKey).([]CallOverrideFunc)
+	if len(cofs) == 0 {
+		return nil, nil, false
+	}
+	// We found a list of overrides; grab the last, and reconstitute a
+	// context that will hide it.
+	f := cofs[len(cofs)-1]
+	ctx = netcontext.WithValue(ctx, &callOverrideKey, cofs[:len(cofs)-1])
+	return f, ctx, true
+}
+
+type logOverrideFunc func(level int64, format string, args ...interface{})
+
+var logOverrideKey = "holds a logOverrideFunc"
+
+func WithLogOverride(ctx netcontext.Context, f logOverrideFunc) netcontext.Context {
+	return netcontext.WithValue(ctx, &logOverrideKey, f)
+}
+
+var appIDOverrideKey = "holds a string, being the full app ID"
+
+func WithAppIDOverride(ctx netcontext.Context, appID string) netcontext.Context {
+	return netcontext.WithValue(ctx, &appIDOverrideKey, appID)
+}
+
+var namespaceKey = "holds the namespace string"
+
+func withNamespace(ctx netcontext.Context, ns string) netcontext.Context {
+	return netcontext.WithValue(ctx, &namespaceKey, ns)
+}
+
+func NamespaceFromContext(ctx netcontext.Context) string {
+	// If there's no namespace, return the empty string.
+	ns, _ := ctx.Value(&namespaceKey).(string)
+	return ns
+}
+
+// FullyQualifiedAppID returns the fully-qualified application ID.
+// This may contain a partition prefix (e.g. "s~" for High Replication apps),
+// or a domain prefix (e.g. "example.com:").
+func FullyQualifiedAppID(ctx netcontext.Context) string {
+	if id, ok := ctx.Value(&appIDOverrideKey).(string); ok {
+		return id
+	}
+	return fullyQualifiedAppID(ctx)
+}
+
+func Logf(ctx netcontext.Context, level int64, format string, args ...interface{}) {
+	if f, ok := ctx.Value(&logOverrideKey).(logOverrideFunc); ok {
+		f(level, format, args...)
+		return
+	}
+	c := fromContext(ctx)
+	if c == nil {
+		panic(errNotAppEngineContext)
+	}
+	logf(c, level, format, args...)
+}
+
+// NamespacedContext wraps a Context to support namespaces.
+func NamespacedContext(ctx netcontext.Context, namespace string) netcontext.Context {
+	return withNamespace(ctx, namespace)
+}
+
+// SetTestEnv sets the env variables for testing background ticket in Flex.
+func SetTestEnv() func() {
+	var environ = []struct {
+		key, value string
+	}{
+		{"GAE_LONG_APP_ID", "my-app-id"},
+		{"GAE_MINOR_VERSION", "067924799508853122"},
+		{"GAE_MODULE_INSTANCE", "0"},
+		{"GAE_MODULE_NAME", "default"},
+		{"GAE_MODULE_VERSION", "20150612t184001"},
+	}
+
+	for _, v := range environ {
+		old := os.Getenv(v.key)
+		os.Setenv(v.key, v.value)
+		v.value = old
+	}
+	return func() { // Restore old environment after the test completes.
+		for _, v := range environ {
+			if v.value == "" {
+				os.Unsetenv(v.key)
+				continue
+			}
+			os.Setenv(v.key, v.value)
+		}
+	}
+}