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

base/message_loop.h

 // Copyright (c) 2012 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.
 
 #ifndef BASE_MESSAGE_LOOP_H_
 #define BASE_MESSAGE_LOOP_H_
 #pragma once
 
 #include <queue>
 #include <string>
@@ skipping 206 matching lines @@
         this, from_here, object);
   }
 
   // Run the message loop.
   void Run();
 
   // Process all pending tasks, windows messages, etc., but don't wait/sleep.
   // 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_; }
 
   // Optional call to connect the thread name with this loop.
   void set_thread_name(const std::string& thread_name) {
     DCHECK(thread_name_.empty()) << "Should not rename this thread!";
     thread_name_ = thread_name;
   }
   const std::string& thread_name() const { return thread_name_; }
@@ skipping 405 matching lines @@
 #endif  // defined(OS_POSIX)
 };
 
 // Do not add any member variables to MessageLoopForIO!  This is important b/c
 // MessageLoopForIO is often allocated via MessageLoop(TYPE_IO).  Any extra
 // data that you need should be stored on the MessageLoop's pump_ instance.
 COMPILE_ASSERT(sizeof(MessageLoop) == sizeof(MessageLoopForIO),
                MessageLoopForIO_should_not_have_extra_member_variables);
 
 #endif  // BASE_MESSAGE_LOOP_H_