Backed out changeset 71445b7c3044 (bug 1292034) for GTest failing APZScrollHandoffTester.ScrollgrabFlingAcceleration1. r=backout

mobile/android/geckoview/src/main/java/org/mozilla/gecko/gfx/StackScroller.java

@@ -261,14 +261,9 @@ public class StackScroller {
         if (mFlywheel && !isFinished()) {
             float oldVelocityX = mScrollerX.mCurrVelocity;
             float oldVelocityY = mScrollerY.mCurrVelocity;
-            boolean sameXDirection = (velocityX == 0) || (oldVelocityX == 0) ||
-                ((velocityX < 0) == (oldVelocityX < 0));
-            boolean sameYDirection = (velocityY == 0) || (oldVelocityY == 0) ||
-                ((velocityY < 0) == (oldVelocityY < 0));
-            if (sameXDirection) {
+            if (Math.signum(velocityX) == Math.signum(oldVelocityX)
+                    && Math.signum(velocityY) == Math.signum(oldVelocityY)) {
                 velocityX += oldVelocityX;
-            }
-            if (sameYDirection) {
                 velocityY += oldVelocityY;
             }
         }