[Telemetry] Always close browser backend in Close()

[Telemetry] Always close browser backend in Close()

We should always close browser backend. If exception 
happens in browser.Close(), e.g., due to device error, 
browser backend will not be closed and then devtools client 
will not be closed. Devtools client will also not be 
garbage collected because chrome_tracing_devtools_manager 
has a map holding all devtool clients. This leads to 
actually 'stale' devtools client still being active. And 
then in the next story run, Telemetry will try to start 
tracing on the actually 'stale' devtools client.

BUG=chromium:595766
Committed: https://chromium.googlesource.com/external/github.com/catapult-project/catapult/+/b81d883874bd78aa5e7011b64d188aaa38589c55

[Zhen Wang, 2016-03-18 21:33:37]

Description was changed from

==========
[Telemetry] Always close browser backend

BUG=chromium:595766
==========

to

==========
[Telemetry] Always close browser backend

We should always close browser backend. If exception 
happens in browser.Close(), e.g., due to device error, 
browser backend will not be closed and then devtools client 
will not be closed. Devtools client will also not be 
garbage collected because chrome_tracing_devtools_manager 
has a map holding all devtool clients. This leads to 
actually 'stale' devtools client still being active. And 
then in the next story run, Telemetry will try to start 
tracing on the actually 'stale' devtools client.

BUG=chromium:595766
==========

[Zhen Wang, 2016-03-18 21:34:06]

Description was changed from

==========
[Telemetry] Always close browser backend

We should always close browser backend. If exception 
happens in browser.Close(), e.g., due to device error, 
browser backend will not be closed and then devtools client 
will not be closed. Devtools client will also not be 
garbage collected because chrome_tracing_devtools_manager 
has a map holding all devtool clients. This leads to 
actually 'stale' devtools client still being active. And 
then in the next story run, Telemetry will try to start 
tracing on the actually 'stale' devtools client.

BUG=chromium:595766
==========

to

==========
[Telemetry] Always close browser backend in Close()

We should always close browser backend. If exception 
happens in browser.Close(), e.g., due to device error, 
browser backend will not be closed and then devtools client 
will not be closed. Devtools client will also not be 
garbage collected because chrome_tracing_devtools_manager 
has a map holding all devtool clients. This leads to 
actually 'stale' devtools client still being active. And 
then in the next story run, Telemetry will try to start 
tracing on the actually 'stale' devtools client.

BUG=chromium:595766
==========

[Zhen Wang, 2016-03-18 21:35:50]

zhenw@chromium.org changed reviewers:
+ nednguyen@google.com

[Zhen Wang, 2016-03-18 21:35:50]

ptal

[nednguyen, 2016-03-18 22:15:33]

lgtm

[Zhen Wang, 2016-03-18 22:15:50]

The CQ bit was checked by zhenw@chromium.org

[commit-bot: I haz the power, 2016-03-18 22:16:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1818593002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1818593002/1

[commit-bot: I haz the power, 2016-03-19 00:24:59]

Description was changed from

==========
[Telemetry] Always close browser backend in Close()

We should always close browser backend. If exception 
happens in browser.Close(), e.g., due to device error, 
browser backend will not be closed and then devtools client 
will not be closed. Devtools client will also not be 
garbage collected because chrome_tracing_devtools_manager 
has a map holding all devtool clients. This leads to 
actually 'stale' devtools client still being active. And 
then in the next story run, Telemetry will try to start 
tracing on the actually 'stale' devtools client.

BUG=chromium:595766
==========

to

==========
[Telemetry] Always close browser backend in Close()

We should always close browser backend. If exception 
happens in browser.Close(), e.g., due to device error, 
browser backend will not be closed and then devtools client 
will not be closed. Devtools client will also not be 
garbage collected because chrome_tracing_devtools_manager 
has a map holding all devtool clients. This leads to 
actually 'stale' devtools client still being active. And 
then in the next story run, Telemetry will try to start 
tracing on the actually 'stale' devtools client.

BUG=chromium:595766

Committed:
https://chromium.googlesource.com/external/github.com/catapult-project/catapu...
==========

[commit-bot: I haz the power, 2016-03-19 00:25:00]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/external/github.com/catapult-project/catapu...