Set InputMethoMananger#mCurRootView to null when window dismissed

InputMethodManager#sInstance is a long live static object so we have to
set its field with right value, otherwise any object referenced by it
cannot be gc including potential activity context.

Now InputMethodManager#mCurRootView is set to null in
InputMethodManager#onPreWindowFocus which is invoked when app's
ViewRootImpl received ViewRootImpl#W#windowfocusChanged from WMS.
However, in the ViewRootImpl#W#windowfocusChanged, mViewAncestor is a
weak reference which get() may returns null sometimes.
One scenario is the ViewRootImpl#W#windowfocusChanged is called after
ActivityThread#handleDestroyActivity. The activity is destroyed and its
ViewRootImpl get GC'd. Then InputMethodManager#onPreWindowFocus won't
get called and InputMethodManager#mCurRootView won't be set to null.

And it is a proper time to set InputMethodManager#mCurRootView to null
when the window it served dismissed.

Fix: 116078227
Test: Break at ActivityThread#handleDestroyActivity and ViewRootImpl#W#windowfocusChanged

Change-Id: I8fabb30f14bcb2cd7019e29b6642b4562d49d248
Signed-off-by: daqi <daqi@xiaomi.com>

core/java/android/view/inputmethod/InputMethodManager.java

@@ -1420,6 +1420,10 @@ public final class InputMethodManager {
                     mServedView.getWindowToken() == appWindowToken) {
                 finishInputLocked();
             }
+            if (mCurRootView != null &&
+                    mCurRootView.getWindowToken() == appWindowToken) {
+                mCurRootView = null;
+            }
         }
     }