[Background Fetch] Cleanup/fix thread safety

content/browser/background_fetch/background_fetch_context.cc

Index: content/browser/background_fetch/background_fetch_context.cc
diff --git a/content/browser/background_fetch/background_fetch_context.cc b/content/browser/background_fetch/background_fetch_context.cc
index 4facffeac426a3d758822190ff7538302bea81c6..a24c1c0535983d086ea73742630f5b0fd48c0cb8 100644
--- a/content/browser/background_fetch/background_fetch_context.cc
+++ b/content/browser/background_fetch/background_fetch_context.cc
@@ -44,29 +44,19 @@ BackgroundFetchContext::BackgroundFetchContext(
           base::MakeUnique<BackgroundFetchDataManager>(browser_context)),
       event_dispatcher_(base::MakeUnique<BackgroundFetchEventDispatcher>(
           std::move(service_worker_context))) {
+  // Although this lives only on the IO thread, it is constructed on UI thread.
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 }
 
 BackgroundFetchContext::~BackgroundFetchContext() {
-  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
 }
 
 void BackgroundFetchContext::InitializeOnIOThread(
     scoped_refptr<net::URLRequestContextGetter> request_context_getter) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
-  request_context_getter_ = request_context_getter;
-}
 
-void BackgroundFetchContext::Shutdown() {
-  DCHECK_CURRENTLY_ON(BrowserThread::UI);
-  BrowserThread::PostTask(
-      BrowserThread::IO, FROM_HERE,
-      base::Bind(&BackgroundFetchContext::ShutdownOnIO, this));
-}
-
-void BackgroundFetchContext::ShutdownOnIO() {
-  DCHECK_CURRENTLY_ON(BrowserThread::IO);
-  active_fetches_.clear();
+  request_context_getter_ = request_context_getter;
 }
 
 void BackgroundFetchContext::StartFetch(
@@ -75,6 +65,7 @@ void BackgroundFetchContext::StartFetch(
     const BackgroundFetchOptions& options,
     blink::mojom::BackgroundFetchService::FetchCallback callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
   data_manager_->CreateRegistration(
       registration_id, requests, options,
       base::BindOnce(&BackgroundFetchContext::DidCreateRegistration, this,
@@ -87,6 +78,8 @@ void BackgroundFetchContext::DidCreateRegistration(
     blink::mojom::BackgroundFetchService::FetchCallback callback,
     blink::mojom::BackgroundFetchError error,
     std::vector<scoped_refptr<BackgroundFetchRequestInfo>> initial_requests) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
   RecordRegistrationCreatedError(error);
   if (error != blink::mojom::BackgroundFetchError::NONE) {
     std::move(callback).Run(error, base::nullopt /* registration */);
@@ -112,6 +105,8 @@ std::vector<std::string>
 BackgroundFetchContext::GetActiveTagsForServiceWorkerRegistration(
     int64_t service_worker_registration_id,
     const url::Origin& origin) const {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
   std::vector<std::string> tags;
   for (const auto& pair : active_fetches_) {
     const BackgroundFetchRegistrationId& registration_id =
@@ -149,6 +144,8 @@ void BackgroundFetchContext::CreateController(
     const BackgroundFetchRegistrationId& registration_id,
     const BackgroundFetchOptions& options,
     std::vector<scoped_refptr<BackgroundFetchRequestInfo>> initial_requests) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
   net::NetworkTrafficAnnotationTag traffic_annotation =
       net::DefineNetworkTrafficAnnotation("background_fetch_context", R"(
         semantics {
@@ -196,6 +193,8 @@ void BackgroundFetchContext::CreateController(
 
 void BackgroundFetchContext::DidCompleteJob(
     BackgroundFetchJobController* controller) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
   const BackgroundFetchRegistrationId& registration_id =
       controller->registration_id();
 
@@ -229,6 +228,8 @@ void BackgroundFetchContext::DidGetSettledFetches(
     bool background_fetch_succeeded,
     std::vector<BackgroundFetchSettledFetch> settled_fetches,
     std::vector<std::unique_ptr<BlobHandle>> blob_handles) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
   if (error != blink::mojom::BackgroundFetchError::NONE) {
     DeleteRegistration(registration_id, std::move(blob_handles));
     return;
@@ -253,6 +254,7 @@ void BackgroundFetchContext::DidGetSettledFetches(
 void BackgroundFetchContext::DeleteRegistration(
     const BackgroundFetchRegistrationId& registration_id,
     const std::vector<std::unique_ptr<BlobHandle>>& blob_handles) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK_GT(active_fetches_.count(registration_id), 0u);
 
   // Delete all persistent information associated with the |registration_id|.