Remove IME surface when occured in multi-window mode

On split-screen, IME is not controlled by the client and it's critical
to remove the surface when hiding the IME.

DisplayImeController doesn't have the access to the actual enabled
InputMethodManager. Instead, this patch introduced a new interface in
InputMethodManagerService to let system UI remove the currently enabled
IME surface when needed.

Bug: 155660756
Test: go/wm-smoke
Test: See reproduce steps in the bug.
Change-Id: I800dbab20aa90fd549ea1c07da85572311ecb7b3

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

@@ -71,4 +71,6 @@ interface IInputMethodManager {
 
     void reportActivityView(in IInputMethodClient parentClient, int childDisplayId,
             in float[] matrixValues);
+
+    void removeImeSurface();
 }

packages/SystemUI/src/com/android/systemui/wm/DisplayImeController.java

@@ -19,11 +19,13 @@ package com.android.systemui.wm;
 import android.animation.Animator;
 import android.animation.AnimatorListenerAdapter;
 import android.animation.ValueAnimator;
+import android.content.Context;
 import android.content.res.Configuration;
 import android.graphics.Point;
 import android.graphics.Rect;
 import android.os.Handler;
 import android.os.RemoteException;
+import android.os.ServiceManager;
 import android.util.Slog;
 import android.util.SparseArray;
 import android.view.IDisplayWindowInsetsController;
@@ -36,6 +38,7 @@ import android.view.WindowInsets;
 import android.view.animation.Interpolator;
 import android.view.animation.PathInterpolator;
 
+import com.android.internal.view.IInputMethodManager;
 import com.android.systemui.TransactionPool;
 import com.android.systemui.dagger.qualifiers.Main;
 
@@ -352,6 +355,16 @@ public class DisplayImeController implements DisplayController.OnDisplaysChanged
                     dispatchEndPositioning(mDisplayId, mCancelled, t);
                     if (mAnimationDirection == DIRECTION_HIDE && !mCancelled) {
                         t.hide(mImeSourceControl.getLeash());
+                        final IInputMethodManager imms = getImms();
+                        if (imms != null) {
+                            try {
+                                // Remove the IME surface to make the insets invisible for
+                                // non-client controlled insets.
+                                imms.removeImeSurface();
+                            } catch (RemoteException e) {
+                                Slog.e(TAG, "Failed to remove IME surface.", e);
+                            }
+                        }
                     }
                     t.apply();
                     mTransactionPool.release(t);
@@ -382,9 +395,9 @@ public class DisplayImeController implements DisplayController.OnDisplaysChanged
          * Called when the IME position is starting to animate.
          *
          * @param hiddenTop The y position of the top of the IME surface when it is hidden.
-         * @param shownTop The y position of the top of the IME surface when it is shown.
-         * @param showing {@code true} when we are animating from hidden to shown, {@code false}
-         *                            when animating from shown to hidden.
+         * @param shownTop  The y position of the top of the IME surface when it is shown.
+         * @param showing   {@code true} when we are animating from hidden to shown, {@code false}
+         *                  when animating from shown to hidden.
          */
         default void onImeStartPositioning(int displayId, int hiddenTop, int shownTop,
                 boolean showing, SurfaceControl.Transaction t) {}
@@ -406,4 +419,9 @@ public class DisplayImeController implements DisplayController.OnDisplaysChanged
         default void onImeEndPositioning(int displayId, boolean cancel,
                 SurfaceControl.Transaction t) {}
     }
+
+    public IInputMethodManager getImms() {
+        return IInputMethodManager.Stub.asInterface(
+                ServiceManager.getService(Context.INPUT_METHOD_SERVICE));
+    }
 }

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

@@ -207,6 +207,7 @@ public class InputMethodManagerService extends IInputMethodManager.Stub
     static final int MSG_HIDE_CURRENT_INPUT_METHOD = 1035;
     static final int MSG_INITIALIZE_IME = 1040;
     static final int MSG_CREATE_SESSION = 1050;
+    static final int MSG_REMOVE_IME_SURFACE = 1060;
 
     static final int MSG_START_INPUT = 2000;
 
@@ -3936,6 +3937,12 @@ public class InputMethodManagerService extends IInputMethodManager.Stub
         }
     }
 
+    @Override
+    public void removeImeSurface() {
+        mContext.enforceCallingPermission(Manifest.permission.INTERNAL_SYSTEM_WINDOW, null);
+        mHandler.sendMessage(mHandler.obtainMessage(MSG_REMOVE_IME_SURFACE));
+    }
+
     @BinderThread
     private void notifyUserAction(@NonNull IBinder token) {
         if (DEBUG) {
@@ -4206,6 +4213,15 @@ public class InputMethodManagerService extends IInputMethodManager.Stub
                 args.recycle();
                 return true;
             }
+            case MSG_REMOVE_IME_SURFACE: {
+                try {
+                    if (mEnabledSession != null && mEnabledSession.session != null) {
+                        mEnabledSession.session.removeImeSurface();
+                    }
+                } catch (RemoteException e) {
+                }
+                return true;
+            }
             // ---------------------------------------------------------
 
             case MSG_START_INPUT: {

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

@@ -1460,6 +1460,12 @@ public final class MultiClientInputMethodManagerService {
             return null;
         }
 
+        @BinderThread
+        @Override
+        public void removeImeSurface() {
+            reportNotSupported();
+        }
+
         @BinderThread
         @Override
         public boolean showSoftInput(