metrics: Add RandomSelector, a class that randomly selects items with odds

chrome/chrome_tests_unit.gypi

 # Copyright 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': {
     'chrome_unit_tests_sources': [
       # histograms.xml is analyzed by AboutFlagsHistogramTest, so this
       # dependency is needed to make commit bots run unit_tests on
       # histograms.xml changes.
       '../tools/metrics/histograms/histograms.xml',
@@ skipping 1299 matching lines @@
       'browser/chromeos/status/data_promo_notification_unittest.cc',
       'browser/chromeos/system/automatic_reboot_manager_unittest.cc',
       'browser/chromeos/system/device_disabling_manager_unittest.cc',
       'browser/chromeos/ui/accessibility_focus_ring_controller_unittest.cc',
       'browser/chromeos/ui/idle_app_name_notification_view_unittest.cc',
       'browser/download/notification/download_item_notification_unittest.cc',
       'browser/extensions/api/enterprise_platform_keys_private/enterprise_platform_keys_private_api_unittest.cc',
       'browser/extensions/api/log_private/syslog_parser_unittest.cc',
       'browser/extensions/updater/local_extension_cache_unittest.cc',
       'browser/metrics/chromeos_metrics_provider_unittest.cc',
+      'browser/metrics/perf/random_selector_unittest.cc',
       'browser/notifications/login_state_notification_blocker_chromeos_unittest.cc',
       'browser/ui/browser_finder_chromeos_unittest.cc',
       # TODO(zturner): Enable this on Windows. See
       # BrowserWithTestWindowTest::SetUp() for a comment explaining why this is
       # broken.
       'browser/ui/views/frame/immersive_mode_controller_ash_unittest.cc',
       'browser/ui/views/frame/web_app_left_header_view_ash_unittest.cc',
       'browser/ui/views/select_file_dialog_extension_unittest.cc',
       'browser/ui/webui/chromeos/login/l10n_util_test_util.cc',
       'browser/ui/webui/chromeos/login/l10n_util_test_util.h',
@@ skipping 1597 matching lines @@
               'dependencies': [
                 '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
               ],
             }],
           ],
         },
       ],
     }],
   ],  # 'conditions'
 }