Create and pass shared-histogram-allocator from browser to renderer.

chrome/browser/metrics/subprocess_metrics_provider.h

+// 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.
+
+#ifndef CHROME_BROWSER_METRICS_SUBPROCESS_METRICS_PROVIDER_H_
+#define CHROME_BROWSER_METRICS_SUBPROCESS_METRICS_PROVIDER_H_
+
+#include <set>
+
+#include "base/gtest_prod_util.h"
+#include "base/id_map.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/scoped_observer.h"
+#include "base/threading/thread_checker.h"
+#include "components/metrics/metrics_provider.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+#include "content/public/browser/render_process_host_observer.h"
+
+namespace base {
+class SharedPersistentMemoryAllocator;
+}
+
+namespace metrics {
+
+// SubprocessMetricsProvider gathers and logs histograms stored in shared
+// memory segments between processes.
+class SubprocessMetricsProvider : public metrics::MetricsProvider,
+                                  public content::NotificationObserver,
+                                  public content::RenderProcessHostObserver {
+ public:
+  SubprocessMetricsProvider();
+  ~SubprocessMetricsProvider() override;
+
+ private:
+  friend class SubprocessMetricsProviderTest;
+  FRIEND_TEST_ALL_PREFIXES(SubprocessMetricsProviderTest, SnapshotMetrics);
+
+  // Indicates subprocess to be monitored with unique id for later reference.
+  void RegisterSubprocessAllocator(
+      int id,
+      scoped_ptr<base::SharedPersistentMemoryAllocator> allocator);
+
+  // Indicates that a subprocess has exited and is thus finished with the
+  // allocator it was using.
+  void DeregisterSubprocessAllocator(int id);
+
+  // Report all histograms of a given allocator to the snapshot-manager.
+  void RecordHistogramSnapshotsFromAllocator(
+      base::HistogramSnapshotManager* snapshot_manager,
+      int id,
+      base::SharedPersistentMemoryAllocator* allocator);
+
+  // metrics::MetricsDataProvider:
+  void RecordHistogramSnapshots(
+      base::HistogramSnapshotManager* snapshot_manager) override;
+
+  // content::NotificationObserver overrides:

[Alexei Svitkine (slow), 2016/03/24 17:29:53]

Nit: Remove " overrides" here and on line 63.

[bcwhite, 2016/03/29 11:53:27]

Done.

+  void Observe(int type,
+               const content::NotificationSource& source,
+               const content::NotificationDetails& details) override;
+
+  // content::RenderProcessHostObserver overrides:
+  void RenderProcessReady(content::RenderProcessHost* host) override;
+  void RenderProcessHostDestroyed(content::RenderProcessHost* host) override;
+
+  // Object for registing notification requests.
+  content::NotificationRegistrar registrar_;
+
+  // All of the shared-persistent-allocators for known sub-processes.
+  using AllocatorByIdMap =
+      IDMap<base::SharedPersistentMemoryAllocator, IDMapOwnPointer, int>;
+  AllocatorByIdMap allocators_by_id_;
+
+  // Allocators that are no longer attached to a subprocess, to be released
+  // once the last data contained therein has been reported.
+  std::vector<scoped_ptr<base::SharedPersistentMemoryAllocator>>
+      allocators_to_release_;
+
+  // Track all observed render processes to un-observe them on exit.
+  ScopedObserver<content::RenderProcessHost, SubprocessMetricsProvider>
+      scoped_observer_;
+
+  base::ThreadChecker thread_checker_;

[Alexei Svitkine (slow), 2016/03/24 17:29:53]

Nit: Make this the first param.

[bcwhite, 2016/03/29 11:53:27]

First param?  To what?  Or do you mean the first member variable?  That doesn't
seem to be the convention elsewhere.

[Alexei Svitkine (slow), 2016/03/29 17:51:24]

Sorry, I did mean first member.

[bcwhite, 2016/03/30 21:25:55]

Done.  Though like I said, there doesn't seem to be any regular practice of
doing that.

+
+  DISALLOW_COPY_AND_ASSIGN(SubprocessMetricsProvider);
+};
+
+}  // namespace metrics
+
+#endif  // CHROME_BROWSER_METRICS_SUBPROCESS_METRICS_PROVIDER_H_