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

base/message_loop.h

Index: base/message_loop.h
diff --git a/base/message_loop.h b/base/message_loop.h
index d78b58addc2019ad46b61e79adf8c918f432a9dd..ccd668fc9172b38a186f518b332655c3e285707a 100644
--- a/base/message_loop.h
+++ b/base/message_loop.h
@@ -224,23 +224,47 @@ class BASE_EXPORT MessageLoop : public base::MessagePump::Delegate {
   // Return as soon as all items that can be run are taken care of.
   void RunAllPending();
 
-  // Signals the Run method to return after it is done processing all pending
-  // messages.  This method may only be called on the same thread that called
-  // Run, and Run must still be on the call stack.
+  // TODO(jbates) remove this. crbug.com/131220. See QuitWhenIdle().
+  void Quit() { QuitWhenIdle(); }
+
+  // Signals the Run method to return when it becomes idle. It will continue to
+  // process pending messages and future messages as long as they are enqueued.
+  // Warning: if the MessageLoop remains busy, it may never quit. Only use this
+  // Quit method when looping procedures (such as web pages) have been shut
+  // down.
   //
-  // Use QuitClosure if you need to Quit another thread's MessageLoop, but note
-  // that doing so is fairly dangerous if the target thread makes nested calls
-  // to MessageLoop::Run.  The problem being that you won't know which nested
-  // run loop you are quitting, so be careful!
-  void Quit();
+  // This method may only be called on the same thread that called Run, and Run
+  // must still be on the call stack.
+  //
+  // Use Quit*Closure variants if you need to Quit another thread's MessageLoop,
+  // but note that doing so is fairly dangerous if the target thread makes
+  // nested calls to MessageLoop::Run.  The problem being that you won't know
+  // which nested run loop you are quitting, so be careful!
+  void QuitWhenIdle();
 
   // This method is a variant of Quit, that does not wait for pending messages
   // to be processed before returning from Run.
   void QuitNow();
 
-  // Invokes Quit on the current MessageLoop when run. Useful to schedule an
-  // arbitrary MessageLoop to Quit.
-  static base::Closure QuitClosure();
+  // This method is a variant of Quit, that only waits for the currently pending
+  // messages to complete. Any new messages after this call will not be
+  // processed and will remain enqueued on the MessageLoop.
+  void QuitAfterPending();

[jar (doing other things), 2012/06/08 01:05:37]

nit: I think this is now too terse.  I read it as:

Do a "Quit" after we have some how finished "Pending."

Perhaps (sadly) better would be:

QuitAfterRunningAllCurrentlyPendingTasks()

or

RunAllCurrentlyPendingTasksAndThenQuit()

[jbates, 2012/06/13 22:11:20]

Removed it since it wasn't adding more than QuitNow or PostTask(QuitNow) already
offered.

+
+  // TODO(jbates) remove this. crbug.com/131220. See QuitWhenIdleClosure().
+  static base::Closure QuitClosure() { return QuitWhenIdleClosure(); }
+
+  // Invokes QuitWhenIdle on the current MessageLoop when run. Useful to

[jar (doing other things), 2012/06/08 01:05:37]

nit: I don't think "current MessageLoop" should be in the comment.  Perhaps you
mean on the "then current..." but that seems similarly confusing.  

Perhaps better is:

Construct a Closure that will call QuitWhenIdle().  Useful to schedule an
arbitrary MessageLoop termination.

[jbates, 2012/06/13 22:11:20]

Done.

+  // schedule an arbitrary MessageLoop to QuitWhenIdle.
+  static base::Closure QuitWhenIdleClosure();
+
+  // Invokes QuitNow on the current MessageLoop when run. Useful to schedule an
+  // arbitrary MessageLoop to QuitNow.
+  static base::Closure QuitNowClosure();
+
+  // Invokes QuitAfterPending on the current MessageLoop when run. Useful to
+  // schedule an arbitrary MessageLoop to QuitAfterPending.
+  static base::Closure QuitAfterPendingClosure();
 
   // Returns the type passed to the constructor.
   Type type() const { return type_; }