Refactor CrashDump*Manager to use a shared CrashDumpObserver.

components/crash/content/browser/crash_dump_observer_android.h

+// Copyright 2015 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 COMPONENTS_CRASH_CONTENT_BROWSER_CRASH_DUMP_OBSERVER_ANDROID_H_
+#define COMPONENTS_CRASH_CONTENT_BROWSER_CRASH_DUMP_OBSERVER_ANDROID_H_
+
+#include <list>
+#include <memory>
+
+#include "base/android/application_status_listener.h"
+#include "base/memory/singleton.h"
+#include "base/memory/weak_ptr.h"
+#include "base/process/kill.h"
+#include "base/process/process.h"
+#include "content/public/browser/browser_child_process_observer.h"
+#include "content/public/browser/file_descriptor_info.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+#include "content/public/common/process_type.h"
+
+namespace breakpad {
+
+// This class centralises the observation of child processes for the
+// purpose of reacting to child process crashes.
+class CrashDumpObserver : public content::BrowserChildProcessObserver,
+                          public content::NotificationObserver {
+ public:
+  class Client {
+   public:
+    Client() {}

[Robert Sesek, 2016/08/04 16:59:01]

For pure virtual interfaces, you don't need to provide a ctor, and if you do not
intend to delete through the interface pointer, move the destructor into
protected:

[Tobias Sargeant, 2016/08/05 14:59:22]

Done.

+    virtual ~Client() {}
+
+    virtual void OnChildStart(int child_process_id,
+                              content::FileDescriptorInfo* mappings) = 0;
+    virtual void OnChildExit(int child_process_id,
+                             base::ProcessHandle pid,
+                             content::ProcessType process_type,
+                             base::TerminationStatus termination_status,
+                             base::android::ApplicationState app_state) = 0;
+
+    DISALLOW_COPY_AND_ASSIGN(Client);
+  };
+
+  static CrashDumpObserver* GetInstance();
+
+  void RegisterClient(Client* client);
+  void UnregisterClient(Client* client);
+
+  void BrowserChildProcessStarted(int child_process_id,
+                                  content::FileDescriptorInfo* mappings);
+
+ private:
+  friend struct base::DefaultSingletonTraits<CrashDumpObserver>;
+
+  CrashDumpObserver();
+  ~CrashDumpObserver() override;
+
+  // content::BrowserChildProcessObserver implementation:
+  void BrowserChildProcessHostDisconnected(
+      const content::ChildProcessData& data) override;
+  void BrowserChildProcessCrashed(const content::ChildProcessData& data,
+                                  int exit_code) override;
+
+  // NotificationObserver implementation:
+  void Observe(int type,
+               const content::NotificationSource& source,
+               const content::NotificationDetails& details) override;
+
+  // Called on child process exit (including crash).
+  void OnChildExit(int child_process_id,
+                   base::ProcessHandle pid,
+                   content::ProcessType process_type,
+                   base::TerminationStatus termination_status,
+                   base::android::ApplicationState app_state);
+
+  content::NotificationRegistrar notification_registrar_;
+
+  base::Lock registered_clients_lock_;
+  std::list<Client*> registered_clients_;

[Robert Sesek, 2016/08/04 16:59:01]

Could you use base::ObserverListThreadSafe instead? (Note that it notifies by
PostTask rather than calling into the observer directly.

[Tobias Sargeant, 2016/08/05 14:59:22]

I looked at this, and I'm not sure that it's compatible with either using a
thread pool, as Bernhard suggested, or (straightforwardly) compatible with the
need to register on one thread, and receive callbacks on another. I can't use
ObserverList either, because it's not threadsafe.

However, thinking about thread safety more in light of your comment, I realised
I had to make some other changes.

+
+  base::WeakPtrFactory<CrashDumpObserver> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(CrashDumpObserver);
+};
+
+}  // namespace breakpad
+
+#endif  // COMPONENTS_CRASH_CONTENT_BROWSER_CRASH_DUMP_OBSERVER_ANDROID_H_