Notify SystemURLRequestContextGetter before shutdown on iOS.

ios/chrome/browser/ios_chrome_io_thread.mm

Index: ios/chrome/browser/ios_chrome_io_thread.mm
diff --git a/ios/chrome/browser/ios_chrome_io_thread.mm b/ios/chrome/browser/ios_chrome_io_thread.mm
index 22fc9c5d63ea76b7f38680d87d3bf72ead16e01d..adb4196f293009bf1205466c7c664b739ee96126 100644
--- a/ios/chrome/browser/ios_chrome_io_thread.mm
+++ b/ios/chrome/browser/ios_chrome_io_thread.mm
@@ -205,6 +205,9 @@ class SystemURLRequestContextGetter : public net::URLRequestContextGetter {
   scoped_refptr<base::SingleThreadTaskRunner> GetNetworkTaskRunner()
       const override;
 
+  // Tells the getter that the URLRequestContext is about to be shut down.
+  void Shutdown();
+
  protected:
   ~SystemURLRequestContextGetter() override;
 
@@ -212,6 +215,7 @@ class SystemURLRequestContextGetter : public net::URLRequestContextGetter {
   IOSChromeIOThread* const
       io_thread_;  // Weak pointer, owned by ApplicationContext.
   scoped_refptr<base::SingleThreadTaskRunner> network_task_runner_;
+  bool shutting_down_;
 
   base::debug::LeakTracker<SystemURLRequestContextGetter> leak_tracker_;
 };
@@ -220,12 +224,15 @@ SystemURLRequestContextGetter::SystemURLRequestContextGetter(
     IOSChromeIOThread* io_thread)
     : io_thread_(io_thread),
       network_task_runner_(
-          web::WebThread::GetTaskRunnerForThread(web::WebThread::IO)) {}
+          web::WebThread::GetTaskRunnerForThread(web::WebThread::IO)),
+      shutting_down_(false) {}
 
 SystemURLRequestContextGetter::~SystemURLRequestContextGetter() {}
 
 net::URLRequestContext* SystemURLRequestContextGetter::GetURLRequestContext() {
   DCHECK_CURRENTLY_ON(web::WebThread::IO);
+  if (shutting_down_)

[mmenke, 2016/07/27 17:23:45]

Could null out io_thread_ instead, don't think it really matters, either way.

[mef, 2016/07/27 18:04:27]

Done.

+    return nullptr;
   DCHECK(io_thread_->globals()->system_request_context.get());
 
   return io_thread_->globals()->system_request_context.get();
@@ -236,6 +243,12 @@ SystemURLRequestContextGetter::GetNetworkTaskRunner() const {
   return network_task_runner_;
 }
 
+void SystemURLRequestContextGetter::Shutdown() {
+  DCHECK_CURRENTLY_ON(web::WebThread::IO);
+  shutting_down_ = true;
+  NotifyContextShuttingDown();
+}
+
 IOSChromeIOThread::Globals::SystemRequestContextLeakChecker::
     SystemRequestContextLeakChecker(Globals* globals)
     : globals_(globals) {
@@ -423,6 +436,7 @@ void IOSChromeIOThread::Init() {
 }
 
 void IOSChromeIOThread::CleanUp() {
+  system_url_request_context_getter_->Shutdown();
   system_url_request_context_getter_ = nullptr;
 
   // Release objects that the net::URLRequestContext could have been pointing