FeatureFlag: quick scrub is now quick switch

- Scale down current task and translate it to the left
- Translate previous task in from the left
- This is a toggle; quick switch again returns to the first task

Currently this is implemented by repurposing onQuickScrub(progress) to update the positions
of the first two pages. This makes tracking velocity a bit difficult; if we want to go down
this path in the long run we should probably track velocity properly on MotionEvents.

Change-Id: I4445b5f08b6e88e71cbb5e30b1f1d45c5f1edc68

src/com/android/launcher3/PagedView.java

@@ -625,6 +625,10 @@ public abstract class PagedView<T extends View & PageIndicator> extends ViewGrou
         mMaxScrollX = computeMaxScrollX();
     }
 
+    public int getMaxScrollX() {
+        return mMaxScrollX;
+    }
+
     protected int computeMaxScrollX() {
         int childCount = getChildCount();
         if (childCount > 0) {
@@ -640,6 +644,10 @@ public abstract class PagedView<T extends View & PageIndicator> extends ViewGrou
         requestLayout();
     }
 
+    public int getPageSpacing() {
+        return mPageSpacing;
+    }
+
     private void dispatchPageCountChanged() {
         if (mPageIndicator != null) {
             mPageIndicator.setMarkersCount(getChildCount());