Support saving browser metrics to disk and reading them during next run.

chrome/browser/metrics/chrome_metrics_service_client.cc

 // 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.
 
 #include "chrome/browser/metrics/chrome_metrics_service_client.h"
 
 #include <stddef.h>
 
 #include <vector>
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram.h"
+#include "base/metrics/persistent_histogram_allocator.h"
 #include "base/path_service.h"
 #include "base/rand_util.h"
 #include "base/strings/string16.h"
 #include "base/threading/platform_thread.h"
 #include "build/build_config.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/google/google_brand.h"
 #include "chrome/browser/metrics/chrome_stability_metrics_provider.h"
 #include "chrome/browser/metrics/metrics_reporting_state.h"
@@ skipping 103 matching lines @@
   PrefService* local_state = g_browser_process->local_state();
   return !local_state->HasPrefPath(metrics::prefs::kMetricsReportingEnabled) &&
          variations::GetVariationParamValue("UMA_EnableCellularLogUpload",
                                             "Enabled") == "true";
 #else
   return false;
 #endif
 }
 
 void RegisterInstallerFileMetricsPreferences(PrefRegistrySimple* registry) {
+  base::GlobalHistogramAllocator* allocator =
+      base::GlobalHistogramAllocator::GetEvenIfDisabled();
+  if (allocator)
+    metrics::FileMetricsProvider::RegisterPrefs(registry, allocator->Name());
+
 #if defined(OS_WIN)
   metrics::FileMetricsProvider::RegisterPrefs(
       registry, installer::kSetupHistogramAllocatorName);
 #endif
 }
 
 void RegisterInstallerFileMetricsProvider(
     metrics::MetricsService* metrics_service) {
-#if defined(OS_WIN)
-  std::unique_ptr<metrics::FileMetricsProvider> file_metrics(
+  // Create an object to monitor files of metrics and include them in reports.
+  std::unique_ptr<metrics::FileMetricsProvider> file_metrics_provider(
       new metrics::FileMetricsProvider(
           content::BrowserThread::GetBlockingPool()
               ->GetTaskRunnerWithShutdownBehavior(
                   base::SequencedWorkerPool::CONTINUE_ON_SHUTDOWN),
           g_browser_process->local_state()));
+
+  // Build the pathname for browser's persistent metrics file. Set it as the
+  // destination for the GlobalHistogramAllocator during process exit and add
+  // it to the file-metrics-provider so one written from a previous run will
+  // be loaded.

[Alexei Svitkine (slow), 2016/05/09 21:24:10]

In this CL, these files are not yet being created right?

If so, please mention this in the comment.

Maybe: TODO(bcwhite): These files are not yet being created. crbug.com/xyz

[bcwhite, 2016/05/10 15:42:40]

Right.  It used to be part but was removed because it's largely unnecessary
(metrics are dumped just before exit) and would cause a startup impact on the
next run.

TODO added.

+  base::FilePath metrics_file;
+  if (base::PathService::Get(chrome::DIR_USER_DATA, &metrics_file)) {
+    base::GlobalHistogramAllocator* allocator =
+        base::GlobalHistogramAllocator::GetEvenIfDisabled();
+    if (allocator) {
+      const char* allocator_name = allocator->Name();
+      metrics_file = metrics_file.AppendASCII(allocator_name)
+                         .AddExtension(FILE_PATH_LITERAL(".pma"));

[Alexei Svitkine (slow), 2016/05/09 21:24:10]

Didn't we have this extension as a constant somewhere?

[bcwhite, 2016/05/10 15:42:40]

Yes.  It's in another CL still in review.  But I'm going to move it right up to
base/ (other CL puts it in content/) so that it's more universally available.

+      allocator->SetPersistentLocation(metrics_file);
+
+      file_metrics_provider->RegisterFile(
+          metrics_file,
+          metrics::FileMetricsProvider::FILE_HISTOGRAMS_ATOMIC,
+          metrics::FileMetricsProvider::ASSOCIATE_PREVIOUS_RUN,
+          allocator_name);
+    }
+  }
+
+#if defined(OS_WIN)
+  // Read metrics file from setup.exe.
   base::FilePath program_dir;
   base::PathService::Get(base::DIR_EXE, &program_dir);
-  file_metrics->RegisterFile(
+  file_metrics_provider->RegisterFile(
       program_dir.AppendASCII(installer::kSetupHistogramAllocatorName)
-          .AddExtension(L".pma"),
+          .AddExtension(FILE_PATH_LITERAL(".pma")),
       metrics::FileMetricsProvider::FILE_HISTOGRAMS_ATOMIC,
+      metrics::FileMetricsProvider::ASSOCIATE_CURRENT_RUN,
       installer::kSetupHistogramAllocatorName);
-  metrics_service->RegisterMetricsProvider(std::move(file_metrics));
 #endif
+
+  // Give the new provider to the metrics service.
+  metrics_service->RegisterMetricsProvider(std::move(file_metrics_provider));
 }
 
 }  // namespace
 
 
 ChromeMetricsServiceClient::ChromeMetricsServiceClient(
     metrics::MetricsStateManager* state_manager)
     : metrics_state_manager_(state_manager),
 #if defined(OS_CHROMEOS)
       chromeos_metrics_provider_(nullptr),
@@ skipping 519 matching lines @@
   }
 }
 
 void ChromeMetricsServiceClient::OnURLOpenedFromOmnibox(OmniboxLog* log) {
   metrics_service_->OnApplicationNotIdle();
 }
 
 bool ChromeMetricsServiceClient::IsUMACellularUploadLogicEnabled() {
   return IsCellularLogicEnabled();
 }