Here's logs from chrome://inspect, 

BackgroundHtmlLoaded  -  741  -  Time elapsed before 0
chos_privatebackground-debug.js:19274 add close controller
chos_privatebackground-debug.js:16585 NaCl module is not initialized yet.
$i18n$input$chrome$mozc$NaclMozc$$postMessage_$ @ chos_privatebackground-debug.js:16585
chos_privatebackground-debug.js:19230 NaclLoaded  -  1136
4chos_privatebackground-debug.js:16585 NaCl module is not initialized yet.
$i18n$input$chrome$mozc$NaclMozc$$postMessage_$ @ chos_privatebackground-debug.js:16585
chos_privatebackground-debug.js:16852 Loading...
chos_privatebackground-debug.js:16852 Loading: 100%
4chos_privatebackground-debug.js:16585 NaCl module is not initialized yet.
$i18n$input$chrome$mozc$NaclMozc$$postMessage_$ @ chos_privatebackground-debug.js:16585
dl.google.com/dl/inputtools/chrome/9.3.0.0/engine.config Failed to load resource: net::ERR_MANDATORY_PROXY_CONFIGURATION_FAILED
3dl.google.com/dl/inputtools/chrome/9.3.0.0/engine.config Failed to load resource: net::ERR_INTERNET_DISCONNECTED



It's hard to tell what happened when because the messages aren't timestamped.

On a device with successful run, log looks slightly different (NaClLoaded is at the end not at the early phase)

chos_privatebackground-debug.js:19230 BackgroundHtmlLoaded  -  220  -  Time elapsed before 0
chos_privatebackground-debug.js:19274 add close controller
chos_privatebackground-debug.js:16585 NaCl module is not initialized yet.
$i18n$input$chrome$mozc$NaclMozc$$postMessage_$ @ chos_privatebackground-debug.js:16585
chos_privatebackground-debug.js:16852 Loading...
chos_privatebackground-debug.js:16852 Loading: 100%
chos_privatebackground-debug.js:19230 NaclLoaded  -  317

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5155214a1679dd8785e7db8bb8cada9b034fff81

commit 5155214a1679dd8785e7db8bb8cada9b034fff81
Author: Yingbing Wu <wuyingbing@chromium.org>
Date: Mon Dec 11 05:08:06 2017

Make first party IME more robust.

When first party IME is terminated unexpectedly, IME api will receive
extension unload event and unregister all IMEs' components of the
extension. Then the IMEs' menu on shelf will disappear.
Although OS restart the first party IME extension at once, however,
the IME menus can't be recovered.

First party IME has more complicated initlization process other than
the normal extension. Should not remove its states when it is crashed.

Adds a condition in OnExtensionUnload to gurad not to unregister
the first party IMEs. And records the extension id, then re-activate
the extension when it reloads.

Bug: 775507, 788247 , 786273 ,761714
Change-Id: I08731d2da82278483b843907aacb8256e0325e88
Reviewed-on: https://chromium-review.googlesource.com/803415
Commit-Queue: Shu Chen <shuchen@chromium.org>
Commit-Queue: Yingbing Wu <wuyingbing@chromium.org>
Reviewed-by: Shu Chen <shuchen@chromium.org>
Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523045}
[modify] https://crrev.com/5155214a1679dd8785e7db8bb8cada9b034fff81/chrome/browser/extensions/api/input_ime/input_ime_api_chromeos.cc
[modify] https://crrev.com/5155214a1679dd8785e7db8bb8cada9b034fff81/chrome/browser/extensions/api/input_ime/input_ime_api_chromeos.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/336b99553640c76a1bb09ee33f49dd575898cc7d

commit 336b99553640c76a1bb09ee33f49dd575898cc7d
Author: Yingbing Wu <wuyingbing@chromium.org>
Date: Wed Dec 13 02:30:57 2017

Make first party IME more robust.

When first party IME is terminated unexpectedly, IME api will receive
extension unload event and unregister all IMEs' components of the
extension. Then the IMEs' menu on shelf will disappear.
Although OS restart the first party IME extension at once, however,
the IME menus can't be recovered.

First party IME has more complicated initlization process other than
the normal extension. Should not remove its states when it is crashed.

Adds a condition in OnExtensionUnload to gurad not to unregister
the first party IMEs. And records the extension id, then re-activate
the extension when it reloads.

Bug: 775507, 788247 , 786273 ,761714
Change-Id: I08731d2da82278483b843907aacb8256e0325e88
Reviewed-on: https://chromium-review.googlesource.com/803415
Commit-Queue: Shu Chen <shuchen@chromium.org>
Commit-Queue: Yingbing Wu <wuyingbing@chromium.org>
Reviewed-by: Shu Chen <shuchen@chromium.org>
Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#523045}(cherry picked from commit 5155214a1679dd8785e7db8bb8cada9b034fff81)
Reviewed-on: https://chromium-review.googlesource.com/818680
Cr-Commit-Position: refs/branch-heads/3282@{#193}
Cr-Branched-From: 5fdc0fab22ce7efd32532ee989b223fa12f8171e-refs/heads/master@{#520840}
[modify] https://crrev.com/336b99553640c76a1bb09ee33f49dd575898cc7d/chrome/browser/extensions/api/input_ime/input_ime_api_chromeos.cc
[modify] https://crrev.com/336b99553640c76a1bb09ee33f49dd575898cc7d/chrome/browser/extensions/api/input_ime/input_ime_api_chromeos.h

The following revision refers to this bug:
  https://chrome-internal.googlesource.com/chromeos/overlays/chromeos-overlay/+/ae409fee2790824062897bbe395e7ff4dfb4647e

commit ae409fee2790824062897bbe395e7ff4dfb4647e
Author: Yingbing Wu <wuyingbing@google.com>
Date: Fri Dec 15 18:10:47 2017

 Issue 635713  has been merged into this issue.