Add UMA metrics for the linux distro.

chrome/browser/metrics/chrome_browser_main_extra_parts_metrics_unittest.cc

 // Copyright 2015 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/metrics/chrome_browser_main_extra_parts_metrics.h"
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/test/histogram_tester.h"
+#include "base/test/scoped_task_environment.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/display/screen.h"
 #include "ui/display/test/test_screen.h"
 #include "ui/events/test/device_data_manager_test_api.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace {
 
 const char kTouchEventFeatureDetectionEnabledHistogramName[] =
     "Touchscreen.TouchEventsEnabled";
 
 }  // namespace
 
 class ChromeBrowserMainExtraPartsMetricsTest : public testing::Test {
  public:
   ChromeBrowserMainExtraPartsMetricsTest();
   ~ChromeBrowserMainExtraPartsMetricsTest() override;
 
  protected:
   // Test API wrapping |device_data_manager_|.
   ui::test::DeviceDataManagerTestAPI device_data_manager_test_api_;
 
  private:
-  // Required by a ChromeBrowserMainExtraPartsMetrics test target.
-  base::MessageLoop message_loop_;
+  // Provides a message loop and allows the use of the task scheduler
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 
   // Dummy screen required by a ChromeBrowserMainExtraPartsMetrics test target.
   display::test::TestScreen test_screen_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeBrowserMainExtraPartsMetricsTest);
 };
 
 ChromeBrowserMainExtraPartsMetricsTest::ChromeBrowserMainExtraPartsMetricsTest()
     : device_data_manager_test_api_() {
   display::Screen::SetScreenInstance(&test_screen_);
@@ skipping 77 matching lines @@
        VerifyTouchEventsEnabledIsRecordedAfterPostBrowserStart) {
   base::HistogramTester histogram_tester;
   ChromeBrowserMainExtraPartsMetrics test_target;
 
   test_target.PostBrowserStart();
   histogram_tester.ExpectTotalCount(
       kTouchEventFeatureDetectionEnabledHistogramName, 1);
 }
 
 #endif  // defined(USE_OZONE) || defined(USE_X11)