adjust frame distance to make scrolling smoother.

Root Cause:
At the end of a scroll gesture, as the velocity drops, the per-frame distance approximation oscillates between 1 px and 0 px, resulting in visible jitter.

Solution:
During the scroll, if the computed distance for the next frame is 0 px, force it to 1 px to keep the animation continuous to  eliminate jitter.

Bug: 425738878

Test:scroll on the activity of app using ListView, observe whether exist jitter.
Change-Id: I1dae1283f9cd084db841c5f807376268eedc75b5
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: MOVZX <movzx@yahoo.com>

core/java/android/widget/OverScroller.java

@@ -670,6 +670,9 @@ public class OverScroller {
         // Current position
         private int mCurrentPosition;
 
+        // last frame position
+        private int mLastPosition;
+
         // Final position
         private int mFinal;
 
@@ -1319,6 +1322,17 @@ public class OverScroller {
 
             mCurrentPosition = mStart + (int) Math.round(distance);
 
+            int deltaDistance = mCurrentPosition - mLastPosition;
+            if (!mFinished && deltaDistance == 0) {
+                int direction = mFinal > mStart ? 1 : -1;
+                mCurrentPosition += direction;
+                if ((direction > 0 && mCurrentPosition > mFinal) ||
+                    (direction < 0 && mCurrentPosition < mFinal)) {
+                    mCurrentPosition = mFinal;
+                }
+            }
+            mLastPosition = mCurrentPosition;
+
             return true;
         }
     }