Rename IBusPanelCandidateWindowHandlerInterface to IMECandidateWindowHandlerInterface.

R=nona@chromium.org
BUG=283612

Review URL: https://codereview.chromium.org/184213002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254441 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254441