Add metrics for Web Components

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/list_view.css',
       'tracing/ui/extras/about_tracing/common.css',
       'tracing/ui/extras/chrome/cc/display_item_list_view.css',
@@ skipping 183 matching lines @@
       'tracing/metrics/system_health/breakdown_tree_helpers.html',
       'tracing/metrics/system_health/clock_sync_latency_metric.html',
       'tracing/metrics/system_health/cpu_time_metric.html',
       'tracing/metrics/system_health/expected_queueing_time_metric.html',
       'tracing/metrics/system_health/loading_metric.html',
       'tracing/metrics/system_health/long_tasks_metric.html',
       'tracing/metrics/system_health/memory_metric.html',
       'tracing/metrics/system_health/power_metric.html',
       'tracing/metrics/system_health/responsiveness_metric.html',
       'tracing/metrics/system_health/utils.html',
+      'tracing/metrics/system_health/web_components_metric.html',
       'tracing/metrics/system_health/webview_startup_metric.html',
       'tracing/metrics/tracing_metric.html',
       'tracing/metrics/v8/execution_metric.html',
       'tracing/metrics/v8/gc_metric.html',
       'tracing/metrics/v8/runtime_stats_metric.html',
       'tracing/metrics/v8/utils.html',
       'tracing/metrics/v8/v8_metrics.html',
       'tracing/metrics/webrtc/webrtc_rendering_metric.html',
       'tracing/model/activity.html',
       'tracing/model/alert.html',
@@ skipping 367 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)',
     ],
   }
 }