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

content/browser/browser_main_runner.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 "content/public/browser/browser_main_runner.h"
 
 #include "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/debug/leak_annotations.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/metrics/persistent_histogram_allocator.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/profiler/scoped_profile.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/time/time.h"
 #include "base/trace_event/heap_profiler_allocation_context_tracker.h"
 #include "base/trace_event/trace_event.h"
 #include "base/tracked_objects.h"
 #include "build/build_config.h"
 #include "components/tracing/trace_config_file.h"
 #include "components/tracing/tracing_switches.h"
@@ skipping 29 matching lines @@
  public:
   BrowserMainRunnerImpl()
       : initialization_started_(false), is_shutdown_(false) {}
 
   ~BrowserMainRunnerImpl() override {
     if (initialization_started_ && !is_shutdown_)
       Shutdown();
   }
 
   int Initialize(const MainFunctionParams& parameters) override {
+    // 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)
+        "BrowserMetrics");
+    base::GlobalHistogramAllocator::Disable();  // Enabled by experiment only.
+
     SCOPED_UMA_HISTOGRAM_LONG_TIMER(
         "Startup.BrowserMainRunnerImplInitializeLongTime");
 
     // TODO(vadimt, yiyaoliu): Remove all tracked_objects references below once
     // crbug.com/453640 is fixed.
     tracked_objects::ThreadData::InitializeThreadContext(kMainThreadName);
     base::trace_event::AllocationContextTracker::SetCurrentThreadName(
         kMainThreadName);
     TRACK_SCOPED_REGION(
         "Startup", "BrowserMainRunnerImpl::Initialize");
@@ skipping 176 matching lines @@
 BrowserMainRunner* BrowserMainRunner::Create() {
   return new BrowserMainRunnerImpl();
 }
 
 // static
 bool BrowserMainRunner::ExitedMainMessageLoop() {
   return g_exited_main_message_loop;
 }
 
 }  // namespace content