Clarified that some autofill interfaces can only be implemented by the system.

Test:  mmm -j frameworks/base/:doc-comment-check-docs

Fixes: 113323194

Change-Id: Ic0bea0e16fca0ce4c67d36f5611587843d7aad9f

core/java/android/service/autofill/CustomDescription.java

@@ -314,7 +314,8 @@ public final class CustomDescription implements Parcelable {
          * is called multiple times passing the same {@code id}, only the last call will be used.
          *
          * @param id resource id of the child view.
-         * @param action action to be performed.
+         * @param action action to be performed. Must be an an implementation provided by the
+         * Android System.
          *
          * @return this builder
          *

core/java/android/service/autofill/OnClickAction.java

@@ -21,6 +21,9 @@ package android.service.autofill;
  *
  * <p>Typically used to switch the visibility of other views in a
  * {@link CustomDescription custom save UI}.
+ *
+ * <p><b>Note:</b> This interface is not meant to be implemented by app developers; only
+ * implementations provided by the Android System can be used in other Autofill APIs.
  */
 public interface OnClickAction {
 }

core/java/android/service/autofill/Sanitizer.java

@@ -21,6 +21,9 @@ package android.service.autofill;
  * <p>Typically used to avoid displaying the save UI for values that are autofilled but reformatted
  * by the app&mdash;for example, if the autofill service sends a credit card number
  * value as "004815162342108" and the app automatically changes it to "0048 1516 2342 108".
+ *
+ * <p><b>Note:</b> This interface is not meant to be implemented by app developers; only
+ * implementations provided by the Android System can be used in other Autofill APIs.
  */
 public interface Sanitizer {
 }

core/java/android/service/autofill/Transformation.java

@@ -20,6 +20,9 @@ package android.service.autofill;
  * template} at runtime, using the values of fields contained in the screen.
  *
  * <p>Typically used by {@link CustomDescription} to provide a customized autofill save UI.
+ *
+ * <p><b>Note:</b> This interface is not meant to be implemented by app developers; only
+ * implementations provided by the Android System can be used in other Autofill APIs.
  */
 public interface Transformation {
 }