Add a new method to set state description

- This CL add a new method setSeekBarStateDescription() to set
  the state of seek bar. Because in some case the description of
  seek bar is not align progress of seek bar.
- Add test case

Bug: 157629483
Test: make -j42 RunSettingsRoboTests
Change-Id: I432e6f9deef59756b0a41244d50aaada1ddac6a9

tests/robotests/src/com/android/settings/widget/SeekBarPreferenceTest.java

@@ -19,6 +19,7 @@ package com.android.settings.widget;
 import static com.google.common.truth.Truth.assertThat;
 
 import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 import android.content.Context;
@@ -110,6 +111,13 @@ public class SeekBarPreferenceTest {
         assertThat(seekBarPreference.isSelectable()).isTrue();
     }
 
+    @Test
+    public void testSetSeekBarStateDescription() {
+        mSeekBarPreference.setSeekBarStateDescription("test");
+
+        verify(mSeekBarPreference).setSeekBarStateDescription("test");
+    }
+
     public static class TestFragment extends PreferenceFragmentCompat {
         @Override
         public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {