Some optimizations in blur outline generator

1) Using ALPHA_8 as the start and end bitmap. This removes one extra
   bitmap generation step
2) Using ByteBuffer on ALPHA_8 bitmap for clipAlpha. This allows us
   to use byteArray instead of intArray for representing pixels

Change-Id: I1b654c439fd491b6b91180ddc562bb97fad857aa
diff --git a/src/com/android/launcher3/CellLayout.java b/src/com/android/launcher3/CellLayout.java
index baccfd1..6714d9f 100644
--- a/src/com/android/launcher3/CellLayout.java
+++ b/src/com/android/launcher3/CellLayout.java
@@ -236,6 +236,7 @@
         for (int i = 0; i < mDragOutlines.length; i++) {
             mDragOutlines[i] = new Rect(-1, -1, -1, -1);
         }
+        mDragOutlinePaint.setColor(getResources().getColor(R.color.outline_color));
 
         // When dragging things around the home screens, we show a green outline of
         // where the item will land. The outlines gradually fade out, leaving a trail