Add appropriate (tiny) offset to widget drops so they land correctly.

Also removed some unused parameters I found on the way.

Bug: 25191623
Change-Id: Ib9a30db106467c114cc8b54a5b13ed3e88162d56
diff --git a/src/com/android/launcher3/CellLayout.java b/src/com/android/launcher3/CellLayout.java
index 0a2a017..94e3e41 100644
--- a/src/com/android/launcher3/CellLayout.java
+++ b/src/com/android/launcher3/CellLayout.java
@@ -902,9 +902,7 @@
                 ((LayoutParams) mShortcutsAndWidgets.getChildAt(0).getLayoutParams()).isFullscreen;
         int left = getPaddingLeft();
         if (!isFullscreen) {
-            int offset = getMeasuredWidth() - getPaddingLeft() - getPaddingRight() -
-                    (mCountX * mCellWidth);
-            left += (int) Math.ceil(offset / 2f);
+            left += (int) Math.ceil(getUnusedHorizontalSpace() / 2f);
         }
         int top = getPaddingTop();
 
@@ -916,6 +914,15 @@
                 top + b - t);
     }
 
+    /**
+     * Returns the amount of space left over after subtracting padding and cells. This space will be
+     * very small, a few pixels at most, and is a result of rounding down when calculating the cell
+     * width in {@link DeviceProfile#calculateCellWidth(int, int)}.
+     */
+    public int getUnusedHorizontalSpace() {
+        return getMeasuredWidth() - getPaddingLeft() - getPaddingRight() - (mCountX * mCellWidth);
+    }
+
     @Override
     protected void onSizeChanged(int w, int h, int oldw, int oldh) {
         super.onSizeChanged(w, h, oldw, oldh);
@@ -1048,8 +1055,8 @@
         return false;
     }
 
-    void visualizeDropLocation(View v, Bitmap dragOutline, int originX, int originY, int cellX,
-            int cellY, int spanX, int spanY, boolean resize, DropTarget.DragObject dragObject) {
+    void visualizeDropLocation(View v, Bitmap dragOutline, int cellX, int cellY, int spanX,
+            int spanY, boolean resize, DropTarget.DragObject dragObject) {
         final int oldDragCellX = mDragCell[0];
         final int oldDragCellY = mDragCell[1];