arc: enable Android tracing from chrome://tracing in dev mode

chromeos/chromeos.gyp

Index: chromeos/chromeos.gyp
diff --git a/chromeos/chromeos.gyp b/chromeos/chromeos.gyp
index 9298870a8f61024fc67858b3cd9a151db6688f92..0049c5b7516d16715699f950b5ea86371f8bb2e1 100644
--- a/chromeos/chromeos.gyp
+++ b/chromeos/chromeos.gyp
@@ -408,6 +408,8 @@
       'timezone/timezone_request.h',
       'timezone/timezone_resolver.cc',
       'timezone/timezone_resolver.h',
+      'trace/arc_trace_agent.cc',

[Daniel Erat, 2017/03/07 15:53:21]

why does this live under //chromeos instead of in //components/arc? creating a
new trace/ subdirectory also seems strange unless you're planning to put more
things here in the future.

[Daniel Erat, 2017/03/08 02:58:40]

unless i'm misreading the code, this new class doesn't have dependencies on
anything besides //base, and it's only used by //content and //chrome (i.e. not
//components/arc). if that's correct, would it be possible to just put it
somewhere within //content? or do you anticipate adding more dependencies later?

yusuke, i think that the location in //chromeos came from your suggestion at
https://codereview.chromium.org/2400163003/ -- can you comment here?

[Earl Ou, 2017/03/08 03:18:08]

Looks OK for me.

1. There is /content/browser/android, and the controller for Chrome tracing on
Android is there. Does it make sense to create /content/browser/arc and put
these two files there?

2. Or maybe we can just put arc_trace_agent.h in /content/browser/tracing,
similar to the other tracing agents, e.g., power_tracing_agent,
etw_tracing_agent.

The solution 2 seems better for me, but would like to hear the comments from
reviewers here.

[Daniel Erat, 2017/03/08 04:58:06]

or maybe /content/browser/chromeos?
yeah, i think that this sounds slightly better to me too if there are already
other agents there.

[Yusuke Sato, 2017/03/08 07:17:44]

I made the suggestion just because I wasn't really sure if content/ OWNERS were
okay with having ARC specific files there (currently there's zero arc_*.{cc,h}
files in content/.) If they're okay, I have no objection to the plan to move the
files to content/.

+      'trace/arc_trace_agent.h',
       'tpm/tpm_password_fetcher.cc',
       'tpm/tpm_password_fetcher.h',
       'tpm/tpm_token_info_getter.cc',