Adding performance tests for HQP that represent importance of optimising HistoryItemsForTerms method

testing/perf/perf_test.gyp

 # Copyright 2013 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.
 
 {
   'targets': [
     {
       'target_name': 'perf_test',
       'type': 'static_library',
       'sources': [
         'perf_test.cc',
+        'scoped_histogram_result_printer.cc',
+        'scoped_histogram_result_printer.h',
       ],
       'dependencies': [
         '../../base/base.gyp:base',
       ],
     },
   ],
 }