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..208b6889d9f88db85b56b96299dc9b0eb076254a 100644
--- a/content/test/test_navigation_observer.cc
+++ b/content/test/test_navigation_observer.cc
@@ -84,11 +84,14 @@ void TestNavigationObserver::WaitForObservation(
 }
 
 void TestNavigationObserver::Wait() {
+  int message_loop_run_id = MessageLoop::current()->next_run_id();

[jar (doing other things), 2012/06/14 04:50:29]

re: discussion of changing API from next_run_id().

Although I think this code works... this hints at why this next_run_id() API
could be problematic.  The issue is that the call has global impact (it changes
some global?), and hence is not re-entrant.  If any of the calls in lines 88-94
happened to induce nested runs, and need to call next_run_id(), then the value
would be "wrong" by the time it was used in line 94.

I think the API needs to be clearly re-entrant... and should  atomically do the
Run() and establish the ID (rather than doing them separately).

[jbates, 2012/06/15 02:20:38]

Done.

   WaitForObservation(
       base::Bind(&MessageLoop::Run,
                  base::Unretained(MessageLoop::current())),
-      base::Bind(&MessageLoop::Quit,
-                 base::Unretained(MessageLoop::current())));
+      base::Bind(&MessageLoop::PostTask,
+                 base::Unretained(MessageLoop::current()),
+                 FROM_HERE,
+                 MessageLoop::QuitNowByIDClosure(message_loop_run_id)));
 }
 
 TestNavigationObserver::TestNavigationObserver(
@@ -131,8 +134,10 @@ 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: