Revert of Remove InputMethodEventHandler.

Revert of Remove InputMethodEventHandler. (patchset #16 id:300001 of https://codereview.chromium.org/2872343003/ )

Reason for revert:
This CL makes TalkBack in Android window unusable. The issue is that after this CL, key event becomes to go through event rewriter in Chrome. TalkBack doesn't expect that events are rewritten by Chrome.

Original issue's description:
> Remove InputMethodEventHandler.
> 
> This change removes InputMethodEventHandler and instead sends the events
> to IME in WindowEventDispatcher::PreDispatchEvent().
> 
> 
> This is a step towards unifying key event processing path in classic ash and
> mus+ash.
> 
> BUG=719269
> 
> Review-Url: https://codereview.chromium.org/2872343003
> Cr-Commit-Position: refs/heads/master@{#472941}
> Committed: https://chromium.googlesource.com/chromium/src/+/9f9dddf904a9eae86f20d0fa3f68c1881a360d80

TBR=sadrul@chromium.org,sky@chromium.org,reillyg@chromium.org,moshayedi@google.com,moshayedi@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=719269

[yawano, 2017-05-26 03:26:17]

Created Revert of Remove InputMethodEventHandler.

[yawano, 2017-05-26 05:37:36]

The CQ bit was checked by yawano@chromium.org

[commit-bot: I haz the power, 2017-05-26 05:38:41]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-05-26 05:42:15]

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

[commit-bot: I haz the power, 2017-05-26 05:42:16]

Try jobs failed on following builders:
  ios-device on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-device/builds...)
  ios-device-xcode-clang on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-device-xcode-...)
  ios-simulator on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-simulator/bui...)
  ios-simulator-xcode-clang on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-simulator-xco...)
  mac_chromium_compile_dbg_ng on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)
  mac_chromium_rel_ng on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[sadrul, 2017-05-26 12:15:44]

On 2017/05/26 03:26:17, yawano wrote:
> Created Revert of Remove InputMethodEventHandler.

Did you file a bug about TalkBack not working?

[yawano, 2017-05-29 01:51:28]

On 2017/05/26 12:15:44, sadrul wrote:
> On 2017/05/26 03:26:17, yawano wrote:
> > Created Revert of Remove InputMethodEventHandler.
> 
> Did you file a bug about TalkBack not working?

No, not yet in crbug.com. Filed at https://crbug.com/727179.

[Hadi, 2017-05-29 14:24:51]

On 2017/05/29 01:51:28, yawano wrote:
> On 2017/05/26 12:15:44, sadrul wrote:
> > On 2017/05/26 03:26:17, yawano wrote:
> > > Created Revert of Remove InputMethodEventHandler.
> > 
> > Did you file a bug about TalkBack not working?
> 
> No, not yet in http://crbug.com. Filed at https://crbug.com/727179.

Created a rebased version of this at https://codereview.chromium.org/2909063002/