Update Contenet Capture API discription

There are missing API description at getServiceComponentName in
ContentCaptureManager. Some errors may occur and an exception may be
thrown. So update the javadoc to remind user to handle.

Fixes: 203368373
Test: make
Change-Id: I979c81c74cda4e50627dc0c83ae7c33b333b9255

core/java/android/view/contentcapture/ContentCaptureManager.java

@@ -483,6 +483,8 @@ public final class ContentCaptureManager {
     /**
      * Returns the component name of the system service that is consuming the captured events for
      * the current user.
+     *
+     * @throws RuntimeException if getting the component name is timed out.
      */
     @Nullable
     public ComponentName getServiceComponentName() {