Make InputMethodManagerService a final class

This CL makes it clear that InputMethodManagerService should never be
extended nor mocked, and compilers and ART should be able to optimize
the code based on such an assumption.

There should be no observable behavior change in the production code.

Bug: 192412909
Test: presubmit
Change-Id: I203554fa2964eac9879a5ba5e23ba2f7087403ed

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

@@ -204,7 +204,7 @@ import java.util.concurrent.atomic.AtomicInteger;
 /**
  * This class provides a system service that manages input methods.
  */
-public class InputMethodManagerService extends IInputMethodManager.Stub
+public final class InputMethodManagerService extends IInputMethodManager.Stub
         implements Handler.Callback {
     static final boolean DEBUG = false;
     static final String TAG = "InputMethodManagerService";