Invalidate IMMS#mCurrentSubtype when upgrading the current IME.

Whenever the package to which the current IME belongs is
modified, IMMS#mCurrentSubtype needs to be invalidated.
Otherwize, InputMethodManager#getCurrentInputMethodSubtype()
continues to return the previously selected subtype.

One example scenario would be to update metadata of a subtype
in a new version of an IME with keeping the same subtypeId.
Suppose imeSubtypeExtraValue was updated from "ABC" to "XYZ".
In this scenario, the subtype in question retrieved with
IMM#getInputMethodList() then InputMethodInfo#getSubtypeAt()
has imeSubtypeExtraValue "XYZ", while the subtype returned
from InputMethodManager#getCurrentInputMethodSubtype() still
has imeSubtypeExtraValue "ABC".

With this CL, IMMS#mCurrentSubtype will be invalidate when
the active IME package is modified.

Bug: 21310194
Bug: 20708002
Change-Id: Ifbb35034d9c8e477ebb5353d2a470dfc1627bbd5
diff --git a/services/core/java/com/android/server/InputMethodManagerService.java b/services/core/java/com/android/server/InputMethodManagerService.java
index 1f6c473..ab0c8a9 100644
--- a/services/core/java/com/android/server/InputMethodManagerService.java
+++ b/services/core/java/com/android/server/InputMethodManagerService.java
@@ -675,6 +675,10 @@
                     // We currently don't have a default input method... is
                     // one now available?
                     changed = chooseNewDefaultIMELocked();
+                } else if (!changed && isPackageModified(curIm.getPackageName())) {
+                    // Even if the current input method is still available, mCurrentSubtype could
+                    // be obsolete when the package is modified in practice.
+                    changed = true;
                 }
 
                 if (changed) {