Ensure network activity is stopped on deallocation.

ios/chrome/browser/web/network_activity_indicator_tab_helper.mm

Index: ios/chrome/browser/web/network_activity_indicator_tab_helper.mm
diff --git a/ios/chrome/browser/web/network_activity_indicator_tab_helper.mm b/ios/chrome/browser/web/network_activity_indicator_tab_helper.mm
index 105ac327d258333b6bfed3044ea8d231dad45b9d..7734e77e7d2f7f1e36b03fa1c8d0e0b0869eb359 100644
--- a/ios/chrome/browser/web/network_activity_indicator_tab_helper.mm
+++ b/ios/chrome/browser/web/network_activity_indicator_tab_helper.mm
@@ -25,7 +25,14 @@ NetworkActivityIndicatorTabHelper::NetworkActivityIndicatorTabHelper(
     NSString* tab_id)
     : web::WebStateObserver(web_state), network_activity_key_([tab_id copy]) {}
 
-NetworkActivityIndicatorTabHelper::~NetworkActivityIndicatorTabHelper() {}
+NetworkActivityIndicatorTabHelper::~NetworkActivityIndicatorTabHelper() {
+  NetworkActivityIndicatorManager* shared_manager =
+      [NetworkActivityIndicatorManager sharedInstance];
+  // Verifies that there is a network task associated with this instance
+  // before stopping a task, so that this method is idempotent.
+  if ([shared_manager numNetworkTasksForGroup:network_activity_key_])
+    [shared_manager stopNetworkTaskForGroup:network_activity_key_];
+}
 
 void NetworkActivityIndicatorTabHelper::DidStartLoading() {
   NetworkActivityIndicatorManager* shared_manager =