Delay PersistentHistogramAllocator creation until it's known to be used.

chrome/browser/chrome_browser_field_trials.cc

 // Copyright (c) 2012 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/chrome_browser_field_trials.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/feature_list.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/persistent_histogram_allocator.h"
 #include "base/strings/string_util.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
+#include "chrome/browser/metrics/chrome_metrics_service_client.h"
 #include "chrome/common/chrome_switches.h"
 #include "components/metrics/metrics_pref_names.h"
 
 #if defined(OS_ANDROID)
 #include "chrome/browser/chrome_browser_field_trials_mobile.h"
 #else
 #include "chrome/browser/chrome_browser_field_trials_desktop.h"
 #endif
 
 namespace {
 
 // Check for feature enabling the use of persistent histogram storage and
 // enable the global allocator if so.
 void InstantiatePersistentHistograms() {
   if (base::FeatureList::IsEnabled(base::kPersistentHistogramsFeature)) {
-    base::GlobalHistogramAllocator::Enable();
+    // Create persistent/shared memory and allow histograms to be stored in
+    // it. Memory that is not actualy used won't be physically mapped by the
+    // system. BrowserMetrics usage, as reported in UMA, peaked around 1.9MiB
+    // as of 2016-02-20.
+    base::GlobalHistogramAllocator::CreateWithLocalMemory(
+        3 << 20,     // 3 MiB
+        0x935DDD43,  // SHA1(BrowserMetrics)
+        ChromeMetricsServiceClient::kBrowserMetricsName);
     base::GlobalHistogramAllocator* allocator =
         base::GlobalHistogramAllocator::Get();
-    DCHECK(allocator);  // Should have been created during startup.
-    allocator->CreateTrackingHistograms(allocator->Name());
+    allocator->CreateTrackingHistograms(
+        ChromeMetricsServiceClient::kBrowserMetricsName);
   }
 }
 
 }  // namespace
 
 ChromeBrowserFieldTrials::ChromeBrowserFieldTrials(
     const base::CommandLine& parsed_command_line)
     : parsed_command_line_(parsed_command_line) {
 }
 
 ChromeBrowserFieldTrials::~ChromeBrowserFieldTrials() {
 }
 
 void ChromeBrowserFieldTrials::SetupFieldTrials() {
   // Field trials that are shared by all platforms.
   InstantiateDynamicTrials();
 
 #if defined(OS_ANDROID)
   chrome::SetupMobileFieldTrials(parsed_command_line_);
 #else
   chrome::SetupDesktopFieldTrials(parsed_command_line_);
 #endif
 }
 
 void ChromeBrowserFieldTrials::InstantiateDynamicTrials() {
   // Persistent histograms must be enabled as soon as possible.
   InstantiatePersistentHistograms();
 }