Persist setup metrics and have Chrome report them during UMA upload.

chrome/installer/setup/installer_metrics.cc

+// Copyright (c) 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.
+
+#include "chrome/installer/setup/installer_metrics.h"
+
+#include "base/files/file_path.h"
+#include "base/files/file_util.h"
+#include "base/metrics/histogram_base.h"
+#include "base/metrics/histogram_persistence.h"
+#include "base/metrics/persistent_memory_allocator.h"
+
+namespace installer {
+
+void BeginPersistentHistogramStorage(const char* name) {

[grt (UTC plus 2), 2016/02/08 18:09:19]

what's the advantage of taking |name| as an arg rather than hardcoding
kSetupHistogramAllocatorName below?

[bcwhite, 2016/02/09 21:08:45]

Each file needs a different preference name because each has a different "last
access" time.

[grt (UTC plus 2), 2016/02/10 16:01:53]

Will setup_main.cc eventually call this multiple times with different names?

[bcwhite, 2016/02/10 16:11:24]

Probably not.  Just seemed a better abstraction.  Would you prefer it
hard-coded?

[grt (UTC plus 2), 2016/02/10 20:28:46]

Sine this file is for exclusive use by the installer, I don't see the benefit to
passing in the value.

[bcwhite, 2016/02/10 21:28:43]

Done.

+  base::SetPersistentHistogramMemoryAllocator(
+      new base::LocalPersistentMemoryAllocator(1 << 20, 0, name));  // 1 MiB
+  base::GetPersistentHistogramMemoryAllocator()->CreateTrackingHistograms(name);
+}
+
+  void EndPersistentHistogramStorage(const base::FilePath& target_path) {

[grt (UTC plus 2), 2016/02/08 18:09:18]

nit: indentation

[bcwhite, 2016/02/09 21:08:46]

Done.

+  // For atomicity, first write to a temporary file and then rename it.
+  // The ImportantFileWriter would be good for this except it supports only
+  // std::string for its data.
+  base::PersistentMemoryAllocator* allocator =
+      base::GetPersistentHistogramMemoryAllocator();
+  allocator->UpdateTrackingHistograms();
+
+  base::FilePath file_path = target_path
+      .AppendASCII(allocator->Name())
+      .AddExtension(L".pma");
+  base::FilePath tmp_file_path;
+  base::DeleteFile(file_path, false);
+
+  if (base::CreateTemporaryFileInDir(file_path.DirName(), &tmp_file_path)) {
+    base::File histograms(tmp_file_path,

[grt (UTC plus 2), 2016/02/08 18:09:18]

#include "base/files/file.h"

[bcwhite, 2016/02/09 21:08:45]

Done.

+                          base::File::FLAG_OPEN | base::File::FLAG_WRITE);
+    if (histograms.IsValid()) {
+      base::PersistentMemoryAllocator* alloc =

[grt (UTC plus 2), 2016/02/08 18:09:18]

is this the same as |allocator| on line 25?

[bcwhite, 2016/02/09 21:08:45]

Heh.  That's what happens when you add code at the top of a file.  Done.

+          base::GetPersistentHistogramMemoryAllocator();
+      int used = static_cast<int>(alloc->used());

[grt (UTC plus 2), 2016/02/08 18:09:19]

base::checked_cast?

[bcwhite, 2016/02/09 21:08:45]

Should be size_t.

[bcwhite, 2016/02/10 15:26:45]

Scratch that.  Write() returns int.  Added comment about how Allocator is
internally restricted to 2GB in size.

[grt (UTC plus 2), 2016/02/10 16:01:53]

File::Write takes its |size| arg as an int and returns an int. It's probably
simplest for |used| to be an int, so either use checked_cast (so that the
process crashes if |used| is ever impossibly large) or do something else safe to
convert the size_t (an unsigned 64-bit int on x64) to int (a signed 32-bit int
everywhere we care about).

+      if (histograms.Write(0, static_cast<const char*>(alloc->data()),
+                           used) == used &&
+          histograms.Flush()) {
+        histograms.Close();
+        if (base::ReplaceFile(tmp_file_path, file_path, nullptr)) {
+          VLOG(1) << "Persistent histograms saved in file: "
+                  << file_path.AsUTF8Unsafe();

[grt (UTC plus 2), 2016/02/08 18:09:18]

.value() instead of AsUTF8Unsafe()

[bcwhite, 2016/02/09 21:08:45]

Done.

+        }
+      }
+    }
+  }
+  base::DeleteFile(tmp_file_path, false);

[grt (UTC plus 2), 2016/02/08 18:09:19]

move this up one line so that the file is only deleted if
CreateTemporaryFileInDir returns true. may as well put an additional
histograms.Close(); above it to handle the case where the file was opened but
the write/flush failed.

[bcwhite, 2016/02/09 21:08:45]

Done.

+}
+
+}  // namespace installer