Fix bug 5434403 - invalidation problem with seek bars at edges

Explicitly invalidate the seek bar thumb area when we change drawable
states for touch down. This prevents the thumb from only being
half-invalidated at the edges since it extends into the view's padding
region.

Change-Id: Icc4e608aca044b2d05f3a9378eced839c03947e6

Author: adamp

core/java/android/widget/AbsSeekBar.java

@@ -335,6 +335,7 @@ public boolean onTouchEvent(MotionEvent event) {
                     mTouchDownX = event.getX();
                 } else {
                     setPressed(true);
+                    invalidate(mThumb.getBounds()); // This may be within the padding region
                     onStartTrackingTouch();
                     trackTouchEvent(event);
                     attemptClaimDrag();
@@ -348,6 +349,7 @@ public boolean onTouchEvent(MotionEvent event) {
                     final float x = event.getX();
                     if (Math.abs(x - mTouchDownX) > mScaledTouchSlop) {
                         setPressed(true);
+                        invalidate(mThumb.getBounds()); // This may be within the padding region
                         onStartTrackingTouch();
                         trackTouchEvent(event);
                         attemptClaimDrag();