Make IME mode indicator on by default.

Before this patch:
* Default: off
* the --enable-ime-mode-indicator flag turns on

After this patch:
* Default: on
* the --disable-ime-mode-indicator flag turns off

BUG=177765

Review URL: https://codereview.chromium.org/68853007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236217 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236217