Replace drainUntilIdle with a dispatch_barrier_sync for Breakpad tests

ios/chrome/test/app/chrome_test_util.mm

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/chrome/test/app/chrome_test_util.h"
 
 #include "base/mac/foundation_util.h"
 #import "breakpad/src/client/ios/BreakpadController.h"
 #include "components/metrics/metrics_pref_names.h"
 #include "components/metrics/metrics_service.h"
@@ skipping 13 matching lines @@
 #import "ios/chrome/browser/ui/commands/UIKit+ChromeExecuteCommand.h"
 #import "ios/chrome/browser/ui/commands/generic_chrome_command.h"
 #import "ios/chrome/browser/ui/main/main_view_controller.h"
 #import "ios/chrome/browser/ui/ntp/new_tab_page_controller.h"
 #import "ios/web/public/test/native_controller_test_util.h"
 
 // Methods to access private members for testing.
 @interface BreakpadController (Testing)
 - (BOOL)isEnabled;
 - (BOOL)isUploadingEnabled;
+- (dispatch_queue_t)queue;

[baxley, 2017/04/20 16:37:42]

Probably outside the scope of this CL... Do you have any thoughts on public APIs
we could use to achieve something similar? Or perhaps things we could make
public APIs?

 @end
 @implementation BreakpadController (Testing)
 - (BOOL)isEnabled {
   return started_;
 }
 - (BOOL)isUploadingEnabled {
   return enableUploads_;
 }
+- (dispatch_queue_t)queue {
+  return queue_;
+}
 @end
 
 namespace {
 // Returns the current tab model.
 TabModel* GetCurrentTabModel() {
   MainController* main_controller = chrome_test_util::GetMainController();
   DCHECK(main_controller);
   BrowserViewController* main_bvc =
       [[main_controller browserViewInformation] mainBVC];
   BrowserViewController* current_bvc =
@@ skipping 142 matching lines @@
 }
 
 bool IsBreakpadReportingEnabled() {
   return [[BreakpadController sharedInstance] isUploadingEnabled];
 }
 
 bool IsFirstLaunchAfterUpgrade() {
   return [chrome_test_util::GetMainController() isFirstLaunchAfterUpgrade];
 }
 
+void WaitForBreakpadQueue() {
+  dispatch_queue_t queue = [[BreakpadController sharedInstance] queue];
+  dispatch_barrier_sync(queue, ^{
+                        });
+}
+
 void OpenChromeFromExternalApp(const GURL& url) {
   [[[UIApplication sharedApplication] delegate]
       applicationWillResignActive:[UIApplication sharedApplication]];
   [GetMainController() setStartupParametersWithURL:url];
 
   [[[UIApplication sharedApplication] delegate]
       applicationDidBecomeActive:[UIApplication sharedApplication]];
 }
 
 }  // namespace chrome_test_util