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:
+  ClientInfo();

[Alexei Svitkine (slow), 2014/07/15 12:53:25]

Nit: Add a destructor decl here and define it out of line.

[gab, 2014/07/15 20:50:06]

Chromium style guide explicitly allows inline destructors when the class is made
strictly of simple members (i.e., POD types or types which are themselves only
made of POD types and have an inline constructor -- I remember that std::string
was explicitly allowed in this scenario):
http://www.chromium.org/developers/coding-style/cpp-dos-and-donts#TOC-When-yo....

In fact clang_compile bots complain when you forget the out-of-line destructor
and your class is considered "complex" (and they don't complain on this CL so it
must be okay IMO).

[grt (UTC plus 2), 2014/07/16 13:52:31]

The style guide allows it for trivial dtors because the compiler can optimize
away the dtor (for the most part). std::string does not have a trivial dtor (it
may need to free allocated memory, so it or one of its constituents must have a
non-implicit dtor), so this struct doesn't have a trivial dtor. Although
Chromium treats std::string as a value type, I don't remember seeing any
discussion that you can use the implicit dtor if your type is
POD-except-for-a-string.

[erikwright (departed), 2014/07/16 15:44:22]

I infer from the fact that the clang style rules allow this inline destructor
that some objective analysis has been done to say that it is reasonable/right to
inline destructors when the only non-POD is a string.

But I don't know of any documentation to that effect.

So I would follow the letter of the style-guide (which dictates an out-of-line
DTOR here) unless I could find the rationale behind the clang rule (probably by
pinging the author) and then update the styleguide to reflect it.

[gab, 2014/07/16 15:51:43]

SG, thanks, I'll just do it to close this argument.

+
+  // The metrics ID of this client: represented as a GUID string.
+  std::string client_id;
+
+  // The installation date: represented as an epoch time in seconds.
+  int64 installation_date;
+
+  // The date on which metrics reporting was enabled: represented as an epoch
+  // time in seconds.
+  int64 reporting_enabled_date;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ClientInfo);
+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_CLIENT_INFO_H_