Remove IME API interface usage from Chromium

Remove IME API interface usage from Chromium

This is a start of 3-side patch to remove interface in Blink
to get notification about IME candidate window change events.

More code cleanups on Chromium side will follow once
the interface is removed from Blink's WebWidgets.h.

Blink side change is
https://codereview.chromium.org/1162853002/

BUG=494856
Committed: https://crrev.com/6ec94146260f880f23ff68013468e2aced644089
Cr-Commit-Position: refs/heads/master@{#332277}

[kochi, 2015-06-01 05:39:49]

The CQ bit was checked by kochi@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-06-01 05:40:01]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1150953003/1

[kochi, 2015-06-01 06:34:20]

kochi@chromium.org changed reviewers:
+ tkent@chromium.org

[kochi, 2015-06-01 06:52:29]

tkent-san

Could you take a look?

[tkent, 2015-06-01 07:02:30]

lgtm by non-owner

[kochi, 2015-06-01 07:09:26]

kochi@chromium.org changed reviewers:
+ avi@chromium.org

[kochi, 2015-06-01 07:09:54]

avi, could you review for content/ onwer?

[commit-bot: I haz the power, 2015-06-01 07:27:04]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-01 07:27:05]

Dry run: This issue passed the CQ dry run.

[Avi (use Gerrit), 2015-06-01 15:04:55]

LGTM

[kochi, 2015-06-01 23:12:36]

The CQ bit was checked by kochi@chromium.org

[commit-bot: I haz the power, 2015-06-01 23:34:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1150953003/1

[commit-bot: I haz the power, 2015-06-02 00:49:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-02 00:50:51]

Patchset 1 (id:??) landed as
https://crrev.com/6ec94146260f880f23ff68013468e2aced644089
Cr-Commit-Position: refs/heads/master@{#332277}