Added metrics to track the time between task switches done via the shelf.

ash/ash.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
     # These files lists are shared with the GN build.
     'ash_sources': [
       'accelerators/accelerator_commands.cc',
@@ skipping 148 matching lines @@
       'host/ash_window_tree_host_x11.h',
       'host/root_window_transformer.h',
       'host/transformer_helper.cc',
       'host/transformer_helper.h',
       'keyboard_uma_event_filter.cc',
       'keyboard_uma_event_filter.h',
       'magnifier/magnification_controller.cc',
       'magnifier/magnification_controller.h',
       'magnifier/partial_magnification_controller.cc',
       'magnifier/partial_magnification_controller.h',
+      'metrics/task_switch_metrics_recorder.cc',
+      'metrics/task_switch_metrics_recorder.h',
+      'metrics/task_switch_time_tracker.cc',
+      'metrics/task_switch_time_tracker.h',
       'metrics/user_metrics_recorder.cc',
       'metrics/user_metrics_recorder.h',
       'multi_profile_uma.cc',
       'multi_profile_uma.h',
       'networking_config_delegate.cc',
       'networking_config_delegate.h',
       'popup_message.cc',
       'popup_message.h',
       'root_window_controller.cc',
       'root_window_controller.h',
@@ skipping 507 matching lines @@
       'test/shelf_item_delegate_manager_test_api.cc',
       'test/shelf_item_delegate_manager_test_api.h',
       'test/shelf_test_api.cc',
       'test/shelf_test_api.h',
       'test/shelf_view_test_api.cc',
       'test/shelf_view_test_api.h',
       'test/shell_test_api.cc',
       'test/shell_test_api.h',
       'test/status_area_widget_test_helper.cc',
       'test/status_area_widget_test_helper.h',
+      'test/task_switch_time_tracker_test_api.cc',
+      'test/task_switch_time_tracker_test_api.h',
       'test/test_activation_delegate.cc',
       'test/test_activation_delegate.h',
       'test/test_lock_state_controller_delegate.cc',
       'test/test_lock_state_controller_delegate.h',
       'test/test_overlay_delegate.cc',
       'test/test_overlay_delegate.h',
       'test/test_screenshot_delegate.cc',
       'test/test_screenshot_delegate.h',
       'test/test_session_state_animator.cc',
       'test/test_session_state_animator.h',
@@ skipping 87 matching lines @@
       'extended_desktop_unittest.cc',
       'focus_cycler_unittest.cc',
       'frame/caption_buttons/frame_caption_button_container_view_unittest.cc',
       'frame/caption_buttons/frame_size_button_unittest.cc',
       'frame/custom_frame_view_ash_unittest.cc',
       'frame/default_header_painter_unittest.cc',
       'host/ash_window_tree_host_x11_unittest.cc',
       'keyboard_overlay/keyboard_overlay_delegate_unittest.cc',
       'keyboard_overlay/keyboard_overlay_view_unittest.cc',
       'magnifier/magnification_controller_unittest.cc',
+      'metrics/task_switch_metrics_recorder_unittest.cc',
+      'metrics/task_switch_time_tracker_unittest.cc',
       'metrics/user_metrics_recorder_unittest.cc',
       'popup_message_unittest.cc',
       'root_window_controller_unittest.cc',
       'screen_util_unittest.cc',
       'shelf/scoped_observer_with_duplicated_sources_unittest.cc',
       'shelf/shelf_layout_manager_unittest.cc',
       'shelf/shelf_model_unittest.cc',
       'shelf/shelf_navigator_unittest.cc',
       'shelf/shelf_tooltip_manager_unittest.cc',
       'shelf/shelf_unittest.cc',
@@ skipping 512 matching lines @@
                   '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
                 ],
               }
             ],
           ],
         },
       ],
     }],
   ],
 }