Add SeekBar property accessors to match available style attributes

Bug 6103624

Change-Id: I7bc863250f3b156cf6663e484baab2c35a949db5

Author: adamp

api/current.txt

@@ -25899,6 +25899,7 @@ package android.widget {
     ctor public AbsSeekBar(android.content.Context, android.util.AttributeSet);
     ctor public AbsSeekBar(android.content.Context, android.util.AttributeSet, int);
     method public int getKeyProgressIncrement();
+    method public android.graphics.drawable.Drawable getThumb();
     method public int getThumbOffset();
     method public void setKeyProgressIncrement(int);
     method public void setThumb(android.graphics.drawable.Drawable);

core/java/android/widget/AbsSeekBar.java

@@ -132,6 +132,16 @@ public void setThumb(Drawable thumb) {
         }
     }
 
+    /**
+     * Return the drawable used to represent the scroll thumb - the component that
+     * the user can drag back and forth indicating the current value by its position.
+     *
+     * @return The current thumb drawable
+     */
+    public Drawable getThumb() {
+        return mThumb;
+    }
+
     /**
      * @see #setThumbOffset(int)
      */