Lock down RemoteInputConnectionImpl#getInputConnection()

This is a mechanical refactoring CL that locks down

  RemoteInputConnectionImpl#getInputConnection()

as a private method.

This is supposed to be helpful to to avoid future misuse of raw
InputConnection instance outside RemoteInputConnectionImpl.

Note that InputMethodManager#isAcceptingText() remains to have the
same observable behavior in this CL.  The key fact is that the
following two fields are updated in an atomic way.

  * RemoteInputConnectionImpl#mInputConnection
  * RemoteInputConnectionImpl#mFinished

Bug: 192412909
Test: presubmit
Change-Id: Ic5fbc6213ad62df95fc0b7eef18bab1fd9fbdbf1

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

@@ -1381,8 +1381,7 @@ public final class InputMethodManager {
     public boolean isAcceptingText() {
         checkFocus();
         synchronized (mH) {
-            return mServedInputConnection != null
-                    && mServedInputConnection.getInputConnection() != null;
+            return mServedInputConnection != null && !mServedInputConnection.isFinished();
         }
     }
 

core/java/com/android/internal/inputmethod/RemoteInputConnectionImpl.java

@@ -86,13 +86,17 @@ public final class RemoteInputConnectionImpl extends IInputContext.Stub {
      * @return {@link InputConnection} to which incoming IPCs will be dispatched.
      */
     @Nullable
-    public InputConnection getInputConnection() {
+    private InputConnection getInputConnection() {
         synchronized (mLock) {
             return mInputConnection;
         }
     }
 
-    private boolean isFinished() {
+    /**
+     * @return {@code true} until the target {@link InputConnection} receives
+     * {@link InputConnection#closeConnection()} as a result of {@link #deactivate()}.
+     */
+    public boolean isFinished() {
         synchronized (mLock) {
             return mFinished;
         }