Adding ExperimentLabels helper class.

chrome/installer/util/experiment_labels.h

+// Copyright 2017 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.
+
+#ifndef CHROME_INSTALLER_UTIL_EXPERIMENT_LABELS_H_
+#define CHROME_INSTALLER_UTIL_EXPERIMENT_LABELS_H_
+
+#include <utility>
+
+#include "base/macros.h"
+#include "base/strings/string16.h"
+#include "base/strings/string_piece.h"
+#include "base/time/time.h"
+
+namespace installer {
+
+// A wrapper around an Omaha "experiment_labels" value. No validation is
+// performed on any values.
+class ExperimentLabels {
+ public:
+  explicit ExperimentLabels(const base::string16& value);
+
+  // Returns the experiment_labels string containing the individual labels.
+  const base::string16& value() const { return value_; }
+
+  // Returns the value for a given label, or an empty StringPiece if it is not
+  // present in the instance's value.
+  base::StringPiece16 GetValueForLabel(base::StringPiece16 label_name) const;

[Patrick Monette, 2017/05/08 15:27:48]

Maybe note that ExperimentLabels must outlive the StringPiece returned?

[grt (UTC plus 2), 2017/05/08 20:15:26]

Done.

+
+  // Sets the value of a given label, overwriting a previous value if found.
+  // The label's expiration date is set to the current time plus |lifetime|.
+  // (A note for the future: if deleting labels is ever needed, this could be
+  // extended to delete if |lifetime| is zero.

[Patrick Monette, 2017/05/08 15:27:48]

I'm not a fan of this comment. If this is ever needed, there's a good chance I'd
recommend an explicit DeleteValue() function, depending on the use-case.

[grt (UTC plus 2), 2017/05/08 20:15:26]

Funny, I had the same thought earlier today -- it'd be a clunky interface. Done.

+  void SetValueForLabel(base::StringPiece16 label_name,
+                        base::StringPiece16 label_value,
+                        base::TimeDelta lifetime);
+
+  // Sets the value of a given label, overwriting a previous value if found.
+  void SetValueForLabel(base::StringPiece16 label_name,
+                        base::StringPiece16 label_value,
+                        base::Time expiration);
+
+ private:
+  // A label's full contents ("name=value|exp") and value within |value_|.

[Patrick Monette, 2017/05/08 15:27:48]

s/exp/expiration

[grt (UTC plus 2), 2017/05/08 20:15:26]

Done.

+  using LabelAndValue = std::pair<base::StringPiece16, base::StringPiece16>;
+
+  // Returns the label and value nameed |label_name|, or empty string pieces if

[Patrick Monette, 2017/05/08 15:27:48]

s/nameed/named

[grt (UTC plus 2), 2017/05/08 20:15:26]

Nice catch! Done.

+  // not found.
+  LabelAndValue FindLabel(base::StringPiece16 label_name) const;
+
+  // The raw experiment_labels string.
+  base::string16 value_;
+
+  DISALLOW_COPY_AND_ASSIGN(ExperimentLabels);
+};
+
+}  // namespace installer
+
+#endif  // CHROME_INSTALLER_UTIL_EXPERIMENT_LABELS_H_