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 1854 matching lines @@
       'browser/metrics/jumplist_metrics_win.cc',
       'browser/metrics/jumplist_metrics_win.h',
       'browser/metrics/metrics_memory_details.cc',
       'browser/metrics/metrics_memory_details.h',
       'browser/metrics/metrics_reporting_state.cc',
       'browser/metrics/metrics_reporting_state.h',
       'browser/metrics/metrics_services_manager.cc',
       'browser/metrics/metrics_services_manager.h',
       'browser/metrics/perf/perf_provider_chromeos.cc',
       'browser/metrics/perf/perf_provider_chromeos.h',
+      'browser/metrics/perf/random_selector.cc',

[dhsharp, 2015/09/15 00:00:21]

Question: should this be under 'chrome_browser_chromeos_sources' instead? That
list says

    # ChromeOS-sources not ending in _chromeos (which would be included in
    # other sections and filtered out for non-ChromeOS platforms.

[Alexei Svitkine (slow), 2015/09/15 15:31:18]

Putting it under chrome_browser_chromeos_sources makes sense to me.

[dhsharp, 2015/09/15 18:21:32]

Done.

+      'browser/metrics/perf/random_selector.h',
       'browser/metrics/signin_status_metrics_provider.cc',
       'browser/metrics/signin_status_metrics_provider.h',
       'browser/metrics/signin_status_metrics_provider_base.cc',
       'browser/metrics/signin_status_metrics_provider_base.h',
       'browser/metrics/signin_status_metrics_provider_chromeos.cc',
       'browser/metrics/signin_status_metrics_provider_chromeos.h',
       'browser/metrics/thread_watcher.cc',
       'browser/metrics/thread_watcher.h',
       'browser/metrics/thread_watcher_android.cc',
       'browser/metrics/thread_watcher_android.h',
@@ skipping 2228 matching lines @@
             '../components/components.gyp:omnibox_browser',
             '../components/components.gyp:rlz',
             '../components/components.gyp:search_engines',
             '../rlz/rlz.gyp:rlz_lib',
           ],
         },
       ],
     }],
   ],
 }