Remove log filtering and add stringsetflag.

common/flag/stringsetflag/stringsetflag.go

+// Copyright 2016 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 stringsetflag provides a flag.Value implementation which resolves
+// multiple args into a stringset.
+package stringsetflag
+
+import (
+        "flag"
+        "fmt"
+        "sort"
+        "strings"
+
+        "github.com/luci/luci-go/common/stringset"
+)
+
+// Flag is a flag.Value implementation which represents an unordered set of
+// strings.
+//
+// For example, this allows you to construct a flag that would behave like:
+//   -myflag Foo
+//   -myflag Bar
+//   -myflag Bar
+//
+// And then myflag.Data.Has("Bar") would be true.
+type Flag struct{ Data stringset.Set }
+
+var _ flag.Value = (*Flag)(nil)
+
+func (f Flag) String() string {
+        if f.Data == nil {
+                return ""
+        }
+        slc := f.Data.ToSlice()
+        sort.Strings(slc)
+        return strings.Join(slc, ",")
+}
+
+// Set implements flag.Value's Set function.
+func (f *Flag) Set(val string) error {
+        if val == "" {
+                return fmt.Errorf("must have an argument value")
+        }
+
+        if f.Data == nil {
+                f.Data = stringset.NewFromSlice(val)
+        } else {
+                f.Data.Add(val)
+        }
+        return nil
+}