Switch to sending IME selection updates early.

- Switching to send out UpdateSelection updates as soon as the change is
  applied in AdapterInputConnection (instead of waiting for Blink)
- Start ignoring the IME updates from Blink if it was caused by an IME event
  sent from AdapterInputConnection by checking requiredAck flag.

BUG=235704,145521

Review URL: https://codereview.chromium.org/24195023

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226301 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226301