[Tracking Requested - why for this release]: Completely broken caret positioning if use Japanese IME

Reproduced with MS-IME and/or ATOK2016 as well.

Reproducible : always

Steps To Reproduce:

1. Open New Tab
2. Click on in-content search
3. Type something in-content search using Japanese IME
   --- now, character displays in address bar as expected
   --- However, no caret display at insertion point of typed text --- BUG!
   --- Instead, the caret is blinking in in-content search field --- BUG!
   --- And also in-content search field does not disappear --- BUG!
4. Commit conversion strings
   --- Caret is still blinking in in-content search field --- BUG!

Actual Results:
as above

Expected Results:
3. Type something in-content search using Japanese IME
--- now, character displays in address bar
--- Caret should be blinking at end of text in address bar
--- in-content search field should disappear
4. Commit conversion strings
--- Caret is blinking at end of text in address bar

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=2809c756574d28c25d031eecd41779d3392c44d4&tochange=226b130b6360f05f7329b3a836177af5bb32fd1d

Regressed by: 226b130b6360 Ed Lee — Bug 1519303 - Add hand-off triggers, add-on icons and bug fixes to Activity Stream r=k88hudson

Ed Lee,
Your patch seems to cause the regression. Can you please look into this?

I'll take a look. Thanks

screencast: https://www.youtube.com/watch?v=BTBge3kB2p4

This looks fixed in latest nightly. I tested using the Japanese IME on Mac and Windows 10.

The fix was part of this commit (bug 1521757 which was included in bug 1522379):
https://hg.mozilla.org/mozilla-central/rev/9fb96d1b0b37