Add base::RunLoop and update ui_test_utils to use it to reduce flakiness

content/test/test_navigation_observer.cc

Index: content/test/test_navigation_observer.cc
diff --git a/content/test/test_navigation_observer.cc b/content/test/test_navigation_observer.cc
index 89ff36fd575feb8ec98c98463596d8c7442c5a2e..92dea533ab041a28332e894049d826a674b7e7f4 100644
--- a/content/test/test_navigation_observer.cc
+++ b/content/test/test_navigation_observer.cc
@@ -14,6 +14,21 @@
 
 namespace content {
 
+namespace {
+
+// Allow some pending tasks and up to |num_deferrals| generations to complete.
+static void DeferQuitWithID(const MessageLoop::RunID& run_id,
+                            int num_deferrals) {
+  if (num_deferrals <= 0) {
+    MessageLoop::current()->QuitNowWithID(run_id);
+  } else {
+    MessageLoop::current()->PostTask(
+        FROM_HERE, base::Bind(&DeferQuitWithID, run_id, num_deferrals - 1));
+  }
+}
+
+}  // namespace
+
 // This class observes |render_view_host| and calls OnJsInjectionReady() of
 // |js_injection_ready_observer| when the time is right to inject JavaScript
 // into the page.
@@ -84,11 +99,13 @@ void TestNavigationObserver::WaitForObservation(
 }
 
 void TestNavigationObserver::Wait() {
+  MessageLoop::RunID run_id = MessageLoop::current()->GetRunID();
+  // Number of times to repost QuitNow task to allow pending tasks to complete:
+  const int num_quit_deferrals = 20;
   WaitForObservation(
-      base::Bind(&MessageLoop::Run,
-                 base::Unretained(MessageLoop::current())),
-      base::Bind(&MessageLoop::Quit,
-                 base::Unretained(MessageLoop::current())));
+      base::Bind(&MessageLoop::RunWithID,
+                 base::Unretained(MessageLoop::current()), run_id),
+      base::Bind(&DeferQuitWithID, run_id, num_quit_deferrals));
 }
 
 TestNavigationObserver::TestNavigationObserver(
@@ -131,8 +148,10 @@ void TestNavigationObserver::Observe(
           ++navigations_completed_ == number_of_navigations_) {
         navigation_started_ = false;
         done_ = true;
-        if (running_)
+        if (running_) {
+          running_ = false;
           done_callback_.Run();
+        }
       }
       break;
     case NOTIFICATION_RENDER_VIEW_HOST_CREATED: