Add mutator utilization metric.

tracing/trace_viewer.gypi

 # Copyright (c) 2015 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': {
     'tracing_css_files': [
       'tracing/ui/base/line_chart.css',
       'tracing/ui/base/list_view.css',
       'tracing/ui/base/pie_chart.css',
@@ skipping 29 matching lines @@
       'tracing/base/event_target.html',
       'tracing/base/extension_registry.html',
       'tracing/base/extension_registry_base.html',
       'tracing/base/extension_registry_basic.html',
       'tracing/base/extension_registry_type_based.html',
       'tracing/base/guid.html',
       'tracing/base/interval_tree.html',
       'tracing/base/iteration_helpers.html',
       'tracing/base/math.html',
       'tracing/base/multi_dimensional_view.html',
+      'tracing/base/piecewise_linear_function.html',
       'tracing/base/quad.html',
       'tracing/base/raf.html',
       'tracing/base/range.html',
       'tracing/base/range_utils.html',
       'tracing/base/rect.html',
       'tracing/base/settings.html',
       'tracing/base/sorted_array_utils.html',
       'tracing/base/statistics.html',
       'tracing/base/task.html',
       'tracing/base/timing.html',
@@ skipping 400 matching lines @@
       'tracing/ui/images/chrome-right.png',
       'tracing/ui/images/ui-states.png',
     ],
     'tracing_files': [
       '<@(tracing_css_files)',
       '<@(tracing_js_html_files)',
       '<@(tracing_img_files)',
     ],
   }
 }