Center drop target button alignment across devices

- Partial re-land of http://ag/18520765

Fix: 229789612
Fix: 231711806
Test: manual
Change-Id: I0630c19901435a30379596378e9c0cd4beb2e764
diff --git a/src/com/android/launcher3/DeviceProfile.java b/src/com/android/launcher3/DeviceProfile.java
index 3ddc90e..95d94fa 100644
--- a/src/com/android/launcher3/DeviceProfile.java
+++ b/src/com/android/launcher3/DeviceProfile.java
@@ -215,6 +215,7 @@
     public int dropTargetHorizontalPaddingPx;
     public int dropTargetVerticalPaddingPx;
     public int dropTargetGapPx;
+    public int dropTargetButtonWorkspaceEdgeGapPx;
 
     // Insets
     private final Rect mInsets = new Rect();
@@ -342,6 +343,8 @@
         dropTargetVerticalPaddingPx = res.getDimensionPixelSize(
                 R.dimen.drop_target_button_drawable_vertical_padding);
         dropTargetGapPx = res.getDimensionPixelSize(R.dimen.drop_target_button_gap);
+        dropTargetButtonWorkspaceEdgeGapPx = res.getDimensionPixelSize(
+                R.dimen.drop_target_button_workspace_edge_gap);
 
         workspaceSpringLoadedBottomSpace =
                 res.getDimensionPixelSize(R.dimen.dynamic_grid_min_spring_loaded_space);