Use ScopedTaskEnvironment instead of MessageLoopForUI in chrome tests.

chrome/browser/ui/cocoa/tabs/alert_indicator_button_cocoa_unittest.mm

 // Copyright 2013 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.
 
 #import "chrome/browser/ui/cocoa/tabs/alert_indicator_button_cocoa.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/mac/scoped_nsobject.h"
-#include "base/message_loop/message_loop.h"
+#include "base/test/scoped_task_environment.h"
 #import "chrome/browser/ui/cocoa/test/cocoa_test_helper.h"
 #include "chrome/common/chrome_switches.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/platform_test.h"
 
 // A simple target to confirm an action was invoked.
 @interface AlertIndicatorButtonTestTarget : NSObject {
  @private
   int count_;
 }
 @property(readonly, nonatomic) int count;
 - (void)incrementCount:(id)sender;
 @end
 
 @implementation AlertIndicatorButtonTestTarget
 @synthesize count = count_;
 - (void)incrementCount:(id)sender {
   ++count_;
 }
 @end
 
 namespace {
 
 class AlertIndicatorButtonTest : public CocoaTest {
  public:
-  AlertIndicatorButtonTest() {
+  AlertIndicatorButtonTest()
+      : scoped_task_environment_(
+            base::test::ScopedTaskEnvironment::MainThreadType::UI) {
     base::CommandLine::ForCurrentProcess()->AppendSwitch(
         std::string("--") + switches::kEnableTabAudioMuting);
 
     // Create the AlertIndicatorButton and add it to a view.
     button_.reset([[AlertIndicatorButton alloc] init]);
     EXPECT_TRUE(button_ != nil);
     [[test_window() contentView] addSubview:button_.get()];
 
     // Initially the button is disabled and showing no indicator.
     EXPECT_EQ(TabAlertState::NONE, [button_ showingAlertState]);
@@ skipping 27 matching lines @@
     // should only be drawing the indicator icon (i.e., there is nothing to
     // mute).  A click should NOT result in another click notification.
     [button_ transitionToAlertState:TabAlertState::TAB_CAPTURING];
     EXPECT_EQ(TabAlertState::TAB_CAPTURING, [button_ showingAlertState]);
     EXPECT_FALSE([button_ isEnabled]);
     [button_ performClick:button_];
     EXPECT_EQ(2, [clickTarget count]);
   }
 
   base::scoped_nsobject<AlertIndicatorButton> button_;
-  base::MessageLoopForUI message_loop_;  // Needed for gfx::Animation.
+
+  // Needed for gfx::Animation.
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 };
 
 TEST_VIEW(AlertIndicatorButtonTest, button_)
 
 }  // namespace