Add SampleMap and use it in SparseHistogram

base/base.gypi

 # 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.
 
 {
   'target_defaults': {
     'variables': {
       'base_target': 0,
     },
     'target_conditions': [
@@ skipping 234 matching lines @@
           'message_loop_proxy_impl.cc',
           'message_loop_proxy_impl.h',
           'message_pump.cc',
           'message_pump.h',
           'message_pump_android.cc',
           'message_pump_android.h',
           'message_pump_default.cc',
           'message_pump_default.h',
           'message_pump_win.cc',
           'message_pump_win.h',
+          'metrics/sample_map.cc',
+          'metrics/sample_map.h',
           'metrics/sample_vector.cc',
           'metrics/sample_vector.h',
           'metrics/bucket_ranges.cc',
           'metrics/bucket_ranges.h',
           'metrics/histogram.cc',
           'metrics/histogram.h',
           'metrics/histogram_base.cc',
           'metrics/histogram_base.h',
           'metrics/histogram_flattener.h',
           'metrics/histogram_samples.cc',
@@ skipping 428 matching lines @@
           # Remove all unnecessary files for build_nexe.py to avoid exceeding
           # command-line-string limitation when building NaCl on Windows.
           ['OS == "win" and >(nacl_untrusted_build)==1', {
               'sources/': [ ['exclude', '\\.h$'] ],
           }],
         ],
       }],
     ],
   },
 }