[Mac] Ensure that browser tests' teardown destroys all browser objects.

chrome/test/base/in_process_browser_test.cc

Index: chrome/test/base/in_process_browser_test.cc
===================================================================
--- chrome/test/base/in_process_browser_test.cc	(revision 137713)
+++ chrome/test/base/in_process_browser_test.cc	(working copy)
@@ -373,20 +373,30 @@
 #endif
 
   QuitBrowsers();
+  CHECK(BrowserList::empty());
 }
 
 void InProcessBrowserTest::QuitBrowsers() {
   if (BrowserList::size() == 0)
     return;
 
-  // Invoke CloseAllBrowsersAndMayExit on a running message loop.
-  // CloseAllBrowsersAndMayExit exits the message loop after everything has been
+  // Invoke AttemptExit on a running message loop.
+  // AttemptExit exits the message loop after everything has been
   // shut down properly.
   MessageLoopForUI::current()->PostTask(FROM_HERE,
                                         base::Bind(&BrowserList::AttemptExit));
   ui_test_utils::RunMessageLoop();
 
 #if defined(OS_MACOSX)
+  // BrowserList::AttemptExit() will attempt to close all browsers by deleting
+  // their tab contents. The last tab contents being removed triggers closing of
+  // the browser window.
+  //
+  // On the Mac, this eventually reaches -windowWillClose: on

[Robert Sesek, 2012/05/18 20:10:15]

nit: just write this as -[BrowserWindowController windowWillClose:]

+  // BrowserWindowController, which will post a deferred -autorelease on itself
+  // to ultimately destroy the Browser object. The line below is necessary to
+  // pump these pending tasks to ensure all Browsers get deleted.

[Robert Sesek, 2012/05/18 20:10:15]

nit: I'd use the word "messages" instead of "tasks" here because the latter
sounds like a MessageLoop task, rather than a Cocoa task.

+  ui_test_utils::RunAllPendingInMessageLoop();
   delete autorelease_pool_;
   autorelease_pool_ = NULL;
 #endif