Retrieve client_id from GoogleUpdateSettings when its missing from Local State.

components/metrics/client_info.h

+// Copyright 2014 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 COMPONENTS_METRICS_CLIENT_INFO_H_
+#define COMPONENTS_METRICS_CLIENT_INFO_H_
+
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/macros.h"
+
+namespace metrics {
+
+// A data object used to pass data from outside the metrics component into the
+// metrics component.
+struct ClientInfo {
+ public:

[Ilya Sherman, 2014/07/11 04:45:41]

nit: Structs are public by default.

[gab, 2014/07/11 20:33:40]

Yes, but since I had a private section below I thought it was weird to leave it
implicitly public here...

+  ClientInfo();
+
+  // The metrics ID of this client: represented as a GUID string.
+  std::string client_id;

[Ilya Sherman, 2014/07/11 04:45:41]

nit: Please leave a blank line between adjacent documented fields.

[gab, 2014/07/11 20:33:40]

Done.

+  // The installation date: represented as an epoch time in seconds.
+  int64 installation_date;
+  // The date on which reporting was enabled: represented as an epoch time in

[Ilya Sherman, 2014/07/11 04:45:41]

nit: "on which reporting was enabled" -> "on which metrics reporting was
enabled"

[gab, 2014/07/11 20:33:40]

Done.

+  // seconds.
+  int64 reporting_enabled_date;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ClientInfo);

[Ilya Sherman, 2014/07/11 04:45:41]

What's wrong with copy or assignment for this class?  Structs typically don't
include this restriction, since they're just simple data containers.

[gab, 2014/07/11 20:33:40]

I think the same argument to put DISALLOW_COPY_AND_ASSIGN on classes (to avoid
unintended copies of multi-member classes) applies on structs which are no
different from classes in that regard.

If I was to remove this I think it would also make sense to not make efforts to
pass ClientInfo by scoped_ptr, but rather just pass it by value, but IMO
avoiding the copies is nice (and this makes it explicit).

The style guide says to either specify an explicit copy constructor or use this
macro:
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Copy_C...

And it also says to use struct in data-only cases:
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Struct...

So IMO struct + DISALLOW_COPY_AND_ASSIGN is correct here.

+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_CLIENT_INFO_H_