Clear IMM references when window dismissed.

Match behavior of removeViewLocked(), where InputMethodManager clears
any strong references to Views, and also clear mCurRootView. Without
this, IMM can leak a DecorView instance after the user has left the
application.

Bug: 6413553
Change-Id: Iad09cf5dbb7f6f156fd39ed243431432e00f8945
2 files changed