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

chrome/installer/setup/installer_metrics.cc

Index: chrome/installer/setup/installer_metrics.cc
diff --git a/chrome/installer/setup/installer_metrics.cc b/chrome/installer/setup/installer_metrics.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b867ffbeca62421e16f2ed292e9244d2777624ce
--- /dev/null
+++ b/chrome/installer/setup/installer_metrics.cc
@@ -0,0 +1,61 @@
+// 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.
+
+#include "chrome/installer/setup/installer_metrics.h"
+
+#include "base/files/file.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"
+#include "chrome/installer/util/util_constants.h"
+
+namespace installer {
+
+void BeginPersistentHistogramStorage() {
+  base::SetPersistentHistogramMemoryAllocator(
+      new base::LocalPersistentMemoryAllocator(
+          1 << 20, 0,  // 1 MiB
+          installer::kSetupHistogramAllocatorName));
+  base::GetPersistentHistogramMemoryAllocator()->CreateTrackingHistograms(
+      installer::kSetupHistogramAllocatorName);
+}
+
+void EndPersistentHistogramStorage(const base::FilePath& target_path) {
+  // 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,
+                          base::File::FLAG_OPEN | base::File::FLAG_WRITE);
+    if (histograms.IsValid()) {
+      // Allocator doesn't support more than 1GB so can never overflow.
+      int used = static_cast<int>(allocator->used());
+      if (histograms.Write(0, static_cast<const char*>(allocator->data()),
+                           used) == used &&
+          histograms.Flush()) {

[Alexei Svitkine (slow), 2016/02/19 18:16:40]

Can you use the utility function WriteFile() to simplify this logic?

https://code.google.com/p/chromium/codesearch#chromium/src/base/files/file_ut...

[bcwhite, 2016/02/19 19:50:14]

Done.

+        histograms.Close();
+        if (base::ReplaceFile(tmp_file_path, file_path, nullptr)) {
+          VLOG(1) << "Persistent histograms saved in file: "
+                  << file_path.value();
+        }
+      }
+      histograms.Close();
+    }
+    base::DeleteFile(tmp_file_path, false);
+  }
+}
+
+}  // namespace installer