Include scheduling-only threads in tracks

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 467 matching lines @@
       'tracing/ui/tracks/object_instance_group_track.html',
       'tracing/ui/tracks/object_instance_track.html',
       'tracing/ui/tracks/power_series_track.html',
       'tracing/ui/tracks/process_memory_dump_track.html',
       'tracing/ui/tracks/process_summary_track.html',
       'tracing/ui/tracks/process_track.html',
       'tracing/ui/tracks/process_track_base.html',
       'tracing/ui/tracks/rect_track.html',
       'tracing/ui/tracks/ruler_track.html',
       'tracing/ui/tracks/sample_track.html',
+      'tracing/ui/tracks/sched_group_track.html',

[charliea (OOO until 10-5), 2016/10/26 21:23:37]

I'm not sure that sched_group_track conveys the right idea here.

All of the existing *_group_tracks
(https://cs.corp.google.com/github/catapult-project/catapult/tracing/tracing/u...)
help display entities called ______Group (e.g. ObjectInstanceGroup, SliceGroup,
AsyncSliceGroup). In this case, we're instead displaying a group of threads that
have nowhere else to live.

Another problem is that this leaks some implementation details of ftrace into
the view code: most people don't know what a sched is, or what a group of
sched's might look like. 

I think that maybe something like other_thread_track.html might be a better
name, although I still don't love it: I just can't think of anything better.
Then, in that file, we describe that this is a place for "other" threads to live
that don't have much information about them.

[John Reck, 2016/10/26 21:55:47]

Done.

       'tracing/ui/tracks/slice_group_track.html',
       'tracing/ui/tracks/slice_track.html',
       'tracing/ui/tracks/spacing_track.html',
       'tracing/ui/tracks/stacked_bars_track.html',
       'tracing/ui/tracks/thread_track.html',
       'tracing/ui/tracks/track.html',
       'tracing/ui/view_specific_brushing_state.html',
       'tracing/value/diagnostics/breakdown.html',
       'tracing/value/diagnostics/diagnostic.html',
       'tracing/value/diagnostics/diagnostic_map.html',
@@ skipping 37 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)',
     ],
   }
 }