[discardable] Don't use weak pointers.

The scheduled purge task now retains the manager, but will not
reschedule itself, ensuring that it will be destroyed.

Bug: 1131857
Change-Id: Ifbb20e0c51902c8104630e35da6b025da1869639
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2586346Reviewed-by: Peng Huang <penghuang@chromium.org>
Commit-Queue: Benoit L <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836130}

components/discardable_memory/client/client_discardable_shared_memory_manager.cc

@@ -257,7 +257,7 @@ ClientDiscardableSharedMemoryManager::AllocateLockedDiscardableMemory(
     task_runner_->PostDelayedTask(
         FROM_HERE,
         base::BindOnce(&ClientDiscardableSharedMemoryManager::ScheduledPurge,
-                       weak_factory_.GetWeakPtr()),
+                       this),
         kScheduledPurgeInterval);
     is_purge_scheduled_ = true;
   }
@@ -444,7 +444,7 @@ void ClientDiscardableSharedMemoryManager::ScheduledPurge() {
     task_runner_->PostDelayedTask(
         FROM_HERE,
         base::BindOnce(&ClientDiscardableSharedMemoryManager::ScheduledPurge,
-                       weak_factory_.GetWeakPtr()),
+                       this),
         kScheduledPurgeInterval);
   }
 }

components/discardable_memory/client/client_discardable_shared_memory_manager.h

@@ -203,9 +203,6 @@ class DISCARDABLE_MEMORY_EXPORT ClientDiscardableSharedMemoryManager
   const bool may_schedule_periodic_purge_;
 
   THREAD_CHECKER(thread_checker_);
-  base::WeakPtrFactory<ClientDiscardableSharedMemoryManager> weak_factory_{
-      this};
-
   DISALLOW_COPY_AND_ASSIGN(ClientDiscardableSharedMemoryManager);
 };