Revert of Refactor History's CommitLaterTask with CancelableCallback

components/history/core/browser/history_backend.cc

Index: components/history/core/browser/history_backend.cc
diff --git a/components/history/core/browser/history_backend.cc b/components/history/core/browser/history_backend.cc
index f3a489a3343522a535eedb5608098f2704b69985..08cacf54212abaa3b3639e655f75878563e0b986 100644
--- a/components/history/core/browser/history_backend.cc
+++ b/components/history/core/browser/history_backend.cc
@@ -114,6 +114,44 @@
   return mv;
 }
 
+// This task is run on a timer so that commits happen at regular intervals
+// so they are batched together. The important thing about this class is that
+// it supports canceling of the task so the reference to the backend will be
+// freed. The problem is that when history is shutting down, there is likely
+// to be one of these commits still pending and holding a reference.
+//
+// The backend can call Cancel to have this task release the reference. The
+// task will still run (if we ever get to processing the event before
+// shutdown), but it will not do anything.
+//
+// Note that this is a refcounted object and is not a task in itself. It should
+// be assigned to a RunnableMethod.
+//
+// TODO(brettw): bug 1165182: This should be replaced with a
+// base::WeakPtrFactory which will handle everything automatically (like we do
+// in ExpireHistoryBackend).
+class CommitLaterTask : public base::RefCounted<CommitLaterTask> {
+ public:
+  explicit CommitLaterTask(HistoryBackend* history_backend)
+      : history_backend_(history_backend) {}
+
+  // The backend will call this function if it is being destroyed so that we
+  // release our reference.
+  void Cancel() { history_backend_ = nullptr; }
+
+  void RunCommit() {
+    if (history_backend_)
+      history_backend_->Commit();
+  }
+
+ private:
+  friend class base::RefCounted<CommitLaterTask>;
+
+  ~CommitLaterTask() {}
+
+  scoped_refptr<HistoryBackend> history_backend_;
+};
+
 QueuedHistoryDBTask::QueuedHistoryDBTask(
     std::unique_ptr<HistoryDBTask> task,
     scoped_refptr<base::SingleThreadTaskRunner> origin_loop,
@@ -179,7 +217,7 @@
       task_runner_(task_runner) {}
 
 HistoryBackend::~HistoryBackend() {
-  DCHECK(scheduled_commit_.IsCancelled()) << "Deleting without cleanup";
+  DCHECK(!scheduled_commit_) << "Deleting without cleanup";
   queued_history_db_tasks_.clear();
 
   // Release stashed embedder object before cleaning up the databases.
@@ -2204,21 +2242,20 @@
 }
 
 void HistoryBackend::ScheduleCommit() {
-  // Non-cancelled means there's an already scheduled commit. Note that
-  // CancelableClosure starts cancelled with the default constructor.
-  if (!scheduled_commit_.IsCancelled())
-    return;
-
-  scheduled_commit_.Reset(
-      base::Bind(&HistoryBackend::Commit, base::Unretained(this)));
-
+  if (scheduled_commit_)
+    return;
+  scheduled_commit_ = new CommitLaterTask(this);
   task_runner_->PostDelayedTask(
-      FROM_HERE, scheduled_commit_.callback(),
+      FROM_HERE,
+      base::Bind(&CommitLaterTask::RunCommit, scheduled_commit_),
       base::TimeDelta::FromSeconds(kCommitIntervalSeconds));
 }
 
 void HistoryBackend::CancelScheduledCommit() {
-  scheduled_commit_.Cancel();
+  if (scheduled_commit_) {
+    scheduled_commit_->Cancel();
+    scheduled_commit_ = nullptr;
+  }
 }
 
 void HistoryBackend::ProcessDBTaskImpl() {