Pass Callback to TaskRunner by value and consume it on invocation (1)

content/browser/dom_storage/dom_storage_task_runner.h

 // Copyright 2013 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 CONTENT_BROWSER_DOM_STORAGE_DOM_STORAGE_TASK_RUNNER_H_
 #define CONTENT_BROWSER_DOM_STORAGE_DOM_STORAGE_TASK_RUNNER_H_
 
+#include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/sequence_checker.h"
 #include "base/sequenced_task_runner.h"
 #include "base/time/time.h"
 #include "content/common/content_export.h"
 
 namespace content {
 
 // DOMStorage uses two task sequences (primary vs commit) to avoid
 // primary access from queuing up behind commits to disk.
 // * Initialization, shutdown, and administrative tasks are performed as
 //   shutdown-blocking primary sequence tasks.
 // * Tasks directly related to the javascript'able interface are performed
 //   as shutdown-blocking primary sequence tasks.
 //   TODO(michaeln): Skip tasks for reading during shutdown.
 // * Internal tasks related to committing changes to disk are performed as
 //   shutdown-blocking commit sequence tasks.
 class CONTENT_EXPORT DOMStorageTaskRunner
     : public base::TaskRunner {
  public:
   enum SequenceID {
     PRIMARY_SEQUENCE,
     COMMIT_SEQUENCE
   };
 
   // The PostTask() and PostDelayedTask() methods defined by TaskRunner
   // post shutdown-blocking tasks on the primary sequence.
   bool PostDelayedTask(const tracked_objects::Location& from_here,
-                       const base::Closure& task,
+                       base::Closure task,
                        base::TimeDelta delay) override = 0;
 
   // Posts a shutdown blocking task to |sequence_id|.
   virtual bool PostShutdownBlockingTask(
       const tracked_objects::Location& from_here,
       SequenceID sequence_id,
-      const base::Closure& task) = 0;
+      base::Closure task) = 0;
 
   virtual void AssertIsRunningOnPrimarySequence() const = 0;
   virtual void AssertIsRunningOnCommitSequence() const = 0;
 
   virtual scoped_refptr<base::SequencedTaskRunner> GetSequencedTaskRunner(
       SequenceID sequence_id) = 0;
 
  protected:
   ~DOMStorageTaskRunner() override {}
 };
 
 // A DOMStorageTaskRunner which manages a primary and a commit sequence.
 class CONTENT_EXPORT DOMStorageWorkerPoolTaskRunner :
       public DOMStorageTaskRunner {
  public:
   // |primary_sequence| and |commit_sequence| should have
   // TaskShutdownBehaviour::BLOCK_SHUTDOWN semantics.
   DOMStorageWorkerPoolTaskRunner(
       scoped_refptr<base::SequencedTaskRunner> primary_sequence,
       scoped_refptr<base::SequencedTaskRunner> commit_sequence);
 
   bool RunsTasksOnCurrentThread() const override;
 
   bool PostDelayedTask(const tracked_objects::Location& from_here,
-                       const base::Closure& task,
+                       base::Closure task,
                        base::TimeDelta delay) override;
 
   bool PostShutdownBlockingTask(const tracked_objects::Location& from_here,
                                 SequenceID sequence_id,
-                                const base::Closure& task) override;
+                                base::Closure task) override;
 
   void AssertIsRunningOnPrimarySequence() const override;
   void AssertIsRunningOnCommitSequence() const override;
 
   scoped_refptr<base::SequencedTaskRunner> GetSequencedTaskRunner(
       SequenceID sequence_id) override;
 
  protected:
   ~DOMStorageWorkerPoolTaskRunner() override;
 
@@ skipping 11 matching lines @@
 // all tasks are scheduled on |task_runner| with zero delay.
 class CONTENT_EXPORT MockDOMStorageTaskRunner :
       public DOMStorageTaskRunner {
  public:
   explicit MockDOMStorageTaskRunner(
       scoped_refptr<base::SequencedTaskRunner> task_runner);
 
   bool RunsTasksOnCurrentThread() const override;
 
   bool PostDelayedTask(const tracked_objects::Location& from_here,
-                       const base::Closure& task,
+                       base::Closure task,
                        base::TimeDelta delay) override;
 
   bool PostShutdownBlockingTask(const tracked_objects::Location& from_here,
                                 SequenceID sequence_id,
-                                const base::Closure& task) override;
+                                base::Closure task) override;
 
   void AssertIsRunningOnPrimarySequence() const override;
   void AssertIsRunningOnCommitSequence() const override;
 
   scoped_refptr<base::SequencedTaskRunner> GetSequencedTaskRunner(
       SequenceID sequence_id) override;
 
  protected:
   ~MockDOMStorageTaskRunner() override;
 
  private:
   const scoped_refptr<base::SequencedTaskRunner> task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(MockDOMStorageTaskRunner);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOM_STORAGE_DOM_STORAGE_TASK_RUNNER_H_