[Offline Prefetch] Backoff support for PrefetchBackgroundTask

components/offline_pages/core/prefetch/prefetch_dispatcher_impl.cc

Index: components/offline_pages/core/prefetch/prefetch_dispatcher_impl.cc
diff --git a/components/offline_pages/core/prefetch/prefetch_dispatcher_impl.cc b/components/offline_pages/core/prefetch/prefetch_dispatcher_impl.cc
index 3c84ca5e937b4883abca3ce91a3b0e33a1b890bf..d85d19bebb2d47ef18dc4bb2fb026e803e492235 100644
--- a/components/offline_pages/core/prefetch/prefetch_dispatcher_impl.cc
+++ b/components/offline_pages/core/prefetch/prefetch_dispatcher_impl.cc
@@ -4,10 +4,20 @@
 
 #include "components/offline_pages/core/prefetch/prefetch_dispatcher_impl.h"
 
+#include "base/bind.h"
+#include "base/task_runner.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "url/gurl.h"
 
 namespace offline_pages {
 
+namespace {
+void DeleteBackgroundTaskHelper(
+    std::unique_ptr<PrefetchDispatcher::ScopedBackgroundTask> task) {
+  task.reset();
+}
+}  // namespace
+
 PrefetchDispatcherImpl::PrefetchDispatcherImpl() {}
 
 PrefetchDispatcherImpl::~PrefetchDispatcherImpl() = default;
@@ -28,11 +38,16 @@ void PrefetchDispatcherImpl::RemovePrefetchURLsByClientId(
 
 void PrefetchDispatcherImpl::BeginBackgroundTask(
     std::unique_ptr<ScopedBackgroundTask> task) {
-  NOTIMPLEMENTED();
+  task_ = std::move(task);
 }
 
-void PrefetchDispatcherImpl::StopBackgroundTask(ScopedBackgroundTask* task) {
-  NOTIMPLEMENTED();
+void PrefetchDispatcherImpl::StopBackgroundTask(bool signaled_by_system) {
+  if (!task_)
+    return;
+  // Delay the deletion till the caller finishes.
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE,
+      base::Bind(&DeleteBackgroundTaskHelper, base::Passed(std::move(task_))));
 }
 
 }  // namespace offline_pages