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

chrome/chrome_browser.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': {
     # All .cc, .h, .m, and .mm files under browser except for:
     # * tests and mocks.
     # * code below browser/chromeos
     # * code below browser/extensions
@@ skipping 906 matching lines @@
     # other sections and filtered out for non-ChromeOS platforms.
     'chrome_browser_chromeos_sources': [
       'browser/media/protected_media_identifier_infobar_delegate.cc',
       'browser/media/protected_media_identifier_infobar_delegate.h',
       'browser/media/protected_media_identifier_permission_context.cc',
       'browser/media/protected_media_identifier_permission_context.h',
       'browser/media/protected_media_identifier_permission_context_factory.cc',
       'browser/media/protected_media_identifier_permission_context_factory.h',
       'browser/metrics/chromeos_metrics_provider.cc',
       'browser/metrics/chromeos_metrics_provider.h',
+      'browser/metrics/perf/random_selector.cc',
+      'browser/metrics/perf/random_selector.h',
       'browser/metrics/perf/windowed_incognito_observer.cc',
       'browser/metrics/perf/windowed_incognito_observer.h',
       # This is technically also dependent on enable_plugins but we don't
       # support ChromeOS with enable_plugins==0.
       'browser/renderer_host/pepper/pepper_platform_verification_message_filter.cc',
       'browser/renderer_host/pepper/pepper_platform_verification_message_filter.h',
     ],
     # Everything but Android, iOS, and CrOS.
     'chrome_browser_desktop_sources': [
       'browser/platform_util.cc',
@@ skipping 3175 matching lines @@
             '../components/components.gyp:omnibox_browser',
             '../components/components.gyp:rlz',
             '../components/components.gyp:search_engines',
             '../rlz/rlz.gyp:rlz_lib',
           ],
         },
       ],
     }],
   ],
 }