Add SampleMap and use it in SparseHistogram

base/base.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,
   },
   'includes': [
     '../build/win_precompile.gypi',
@@ skipping 422 matching lines @@
         'memory/scoped_ptr_unittest.nc',
         'memory/scoped_vector_unittest.cc',
         'memory/singleton_unittest.cc',
         'memory/weak_ptr_unittest.cc',
         'memory/weak_ptr_unittest.nc',
         'message_loop_proxy_impl_unittest.cc',
         'message_loop_proxy_unittest.cc',
         'message_loop_unittest.cc',
         'message_pump_glib_unittest.cc',
         'message_pump_libevent_unittest.cc',
+        'metrics/sample_map_unittest.cc',
         'metrics/sample_vector_unittest.cc',
         'metrics/bucket_ranges_unittest.cc',
         'metrics/field_trial_unittest.cc',
         'metrics/histogram_unittest.cc',
         'metrics/sparse_histogram_unittest.cc',
         'metrics/stats_table_unittest.cc',
         'metrics/statistics_recorder_unittest.cc',
         'observer_list_unittest.cc',
         'os_compat_android_unittest.cc',
         'path_service_unittest.cc',
@@ skipping 601 matching lines @@
                 '--result', '<@(_outputs)',
                 '--isolate', 'base_unittests.isolate',
               ],
             },
           ],
         },
       ],
     }],
   ],
 }