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

chrome/browser/ui/views/tabs/tab_drag_controller_interactive_uitest_win.cc

 // 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.
 
 #include "chrome/browser/ui/views/tabs/tab_drag_controller_interactive_uitest.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/property_bag.h"
@@ skipping 229 matching lines @@
   delete to_delete;
 
   // Should still be dragging.
   ASSERT_TRUE(tab_strip->IsDragSessionActive());
   ASSERT_TRUE(TabDragController::IsActive());
 
   // Release the mouse.
   ASSERT_TRUE(ui_test_utils::SendMouseEventsSync(
                   ui_controls::LEFT, ui_controls::UP));
 
+  // Wait for the effects of the mouse event to settle.
+  ui_test_utils::RunAllPendingInMessageLoop();
+
   // Releasing the mouse should destroy the existing browser and create a new
   // one.
   ASSERT_EQ(1u, BrowserList::size());
   Browser* new_browser = *BrowserList::begin();
   EXPECT_NE(new_browser, browser());
 
   ASSERT_FALSE(GetTabStripForBrowser(new_browser)->IsDragSessionActive());
   ASSERT_FALSE(TabDragController::IsActive());
 
   EXPECT_EQ("0", IDString(new_browser->tab_strip_model()));
@@ skipping 85 matching lines @@
   ASSERT_TRUE(ui_test_utils::SendKeyPressSync(
       browser2, ui::VKEY_ESCAPE, false, false, false, false));
 
   ASSERT_FALSE(tab_strip->IsDragSessionActive());
   ASSERT_FALSE(tab_strip2->IsDragSessionActive());
   ASSERT_FALSE(TabDragController::IsActive());
   ASSERT_EQ(2u, BrowserList::size());
   EXPECT_EQ("0 1", IDString(browser()->tab_strip_model()));
   EXPECT_EQ("100", IDString(browser2->tab_strip_model()));
 }