Fixing issue where you couldn't drag an item multiple pages (issue 10754544)

-> This was caused by a strange race condition. The page snap time was equal to
   the delay to recheck whether to snap (in DragController). This meant that
   scrollRight()/Left() would get called, and the scroller would be finished
   however, the final computeScrollHelper() hadn't been called, so the mCurrentPage
   hadn't yet been incremented.
-> Fixed the underlying race condition.
-> Added suitable gap (150 ms) between the two delays.

Change-Id: If700eb9e14d77a174e4395ca6933119bdb0da768

src/com/android/launcher3/PagedView.java

@@ -2153,19 +2153,11 @@ public abstract class PagedView extends ViewGroup implements ViewGroup.OnHierarc
     }
 
     public void scrollLeft() {
-        if (mScroller.isFinished()) {
-            if (mCurrentPage > 0) snapToPage(mCurrentPage - 1);
-        } else {
-            if (mNextPage > 0) snapToPage(mNextPage - 1);
-        }
+        if (getNextPage() > 0) snapToPage(getNextPage() - 1);
     }
 
     public void scrollRight() {
-        if (mScroller.isFinished()) {
-            if (mCurrentPage < getChildCount() -1) snapToPage(mCurrentPage + 1);
-        } else {
-            if (mNextPage < getChildCount() -1) snapToPage(mNextPage + 1);
-        }
+        if (getNextPage() < getChildCount() -1) snapToPage(getNextPage() + 1);
     }
 
     public int getPageForView(View v) {