Support background users to call IMM#getLastInputMethodSubtype()

This is a follow up CL to my previous CL [1], which let query APIs
defined in InputMethodManager support background users.

With this CL,

  InputMethodManager#getLastInputMethodSubtype()

is also fully supported under multi-user / multi-profile environment.

 [1]: I192a0f5a1375170d17a4c08af94f23966dbaea8b
      7f8ee4b9dd

Bug: 34886274
Bug: 122164939
Test: atest CtsInputMethodTestCases:InputMethodSubtypeTest
Change-Id: I48f57dc7184e85bdb422fd9d1d56e60381654125

core/java/android/view/inputmethod/IInputMethodManagerInvoker.java

@@ -101,9 +101,9 @@ final class IInputMethodManagerInvoker {
 
     @AnyThread
     @Nullable
-    InputMethodSubtype getLastInputMethodSubtype() {
+    InputMethodSubtype getLastInputMethodSubtype(@UserIdInt int userId) {
         try {
-            return mTarget.getLastInputMethodSubtype();
+            return mTarget.getLastInputMethodSubtype(userId);
         } catch (RemoteException e) {
             throw e.rethrowFromSystemServer();
         }

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

@@ -3517,7 +3517,7 @@ public final class InputMethodManager {
 
     @Nullable
     public InputMethodSubtype getLastInputMethodSubtype() {
-        return mServiceInvoker.getLastInputMethodSubtype();
+        return mServiceInvoker.getLastInputMethodSubtype(UserHandle.myUserId());
     }
 
     /**

core/java/com/android/internal/view/IInputMethodManager.aidl

@@ -50,7 +50,9 @@ interface IInputMethodManager {
     List<InputMethodSubtype> getEnabledInputMethodSubtypeList(in @nullable String imiId,
             boolean allowsImplicitlySelectedSubtypes, int userId);
 
-    @nullable InputMethodSubtype getLastInputMethodSubtype();
+    @JavaPassthrough(annotation="@android.annotation.RequiresPermission(value = "
+            + "android.Manifest.permission.INTERACT_ACROSS_USERS_FULL, conditional = true)")
+    InputMethodSubtype getLastInputMethodSubtype(int userId);
 
     boolean showSoftInput(in IInputMethodClient client, @nullable IBinder windowToken, int flags,
             in @nullable ResultReceiver resultReceiver, int reason);

services/core/java/com/android/server/inputmethod/InputMethodManagerService.java

@@ -4160,12 +4160,20 @@ public final class InputMethodManagerService extends IInputMethodManager.Stub
     }
 
     @Override
-    public InputMethodSubtype getLastInputMethodSubtype() {
+    public InputMethodSubtype getLastInputMethodSubtype(@UserIdInt int userId) {
+        if (UserHandle.getCallingUserId() != userId) {
+            mContext.enforceCallingPermission(Manifest.permission.INTERACT_ACROSS_USERS_FULL, null);
+        }
         synchronized (ImfLock.class) {
-            if (!calledFromValidUserLocked()) {
-                return null;
+            if (mSettings.getCurrentUserId() == userId) {
+                return mSettings.getLastInputMethodSubtypeLocked();
             }
-            return mSettings.getLastInputMethodSubtypeLocked();
+
+            final ArrayMap<String, InputMethodInfo> methodMap = queryMethodMapForUser(userId);
+            final InputMethodSettings settings = new InputMethodSettings(
+                    mContext.getResources(), mContext.getContentResolver(), methodMap,
+                    userId, false);
+            return settings.getLastInputMethodSubtypeLocked();
         }
     }