Revert of Remove the unnecessary PathExists check for IME extension file paths. ...

Revert of Remove the unnecessary PathExists check for IME extension file paths. (https://codereview.chromium.org/426133004/)

Reason for revert:
Unlikely but one of the view chromeos specific changes that might have broken ChromeOS tests:

http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Ozone%20Tests%20%282%29/builds/634

http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%282%29/builds/25631

Original issue's description:
> Remove the unnecessary PathExists check for IME extension file paths.
> And makes sure the key events can bypass extension if no listener is added for onKeyEvent.
>
> BUG=398289,397971
> TEST=Verified on sandbox.
>
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=286785

TBR=yukishiino@chromium.org,shuchen@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=398289,397971

Review URL: https://codereview.chromium.org/417063003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286812 0039d316-1c4b-4281-b951-d872f2087c98