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diff --git a/components/newtab/dropPreview.js b/components/newtab/dropPreview.js
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+#ifdef 0
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+#endif
+
+/**
+ * This singleton provides the ability to re-arrange the current grid to
+ * indicate the transformation that results from dropping a cell at a certain
+ * position.
+ */
+var gDropPreview = {
+  /**
+   * Rearranges the sites currently contained in the grid when a site would be
+   * dropped onto the given cell.
+   * @param aCell The drop target cell.
+   * @return The re-arranged array of sites.
+   */
+  rearrange: function DropPreview_rearrange(aCell) {
+    let sites = gGrid.sites;
+
+    // Insert the dragged site into the current grid.
+    this._insertDraggedSite(sites, aCell);
+
+    // After the new site has been inserted we need to correct the positions
+    // of all pinned tabs that have been moved around.
+    this._repositionPinnedSites(sites, aCell);
+
+    return sites;
+  },
+
+  /**
+   * Inserts the currently dragged site into the given array of sites.
+   * @param aSites The array of sites to insert into.
+   * @param aCell The drop target cell.
+   */
+  _insertDraggedSite: function DropPreview_insertDraggedSite(aSites, aCell) {
+    let dropIndex = aCell.index;
+    let draggedSite = gDrag.draggedSite;
+
+    // We're currently dragging a site.
+    if (draggedSite) {
+      let dragCell = draggedSite.cell;
+      let dragIndex = dragCell.index;
+
+      // Move the dragged site into its new position.
+      if (dragIndex != dropIndex) {
+        aSites.splice(dragIndex, 1);
+        aSites.splice(dropIndex, 0, draggedSite);
+      }
+    // We're handling an external drag item.
+    } else {
+      aSites.splice(dropIndex, 0, null);
+    }
+  },
+
+  /**
+   * Correct the position of all pinned sites that might have been moved to
+   * different positions after the dragged site has been inserted.
+   * @param aSites The array of sites containing the dragged site.
+   * @param aCell The drop target cell.
+   */
+  _repositionPinnedSites:
+    function DropPreview_repositionPinnedSites(aSites, aCell) {
+
+    // Collect all pinned sites.
+    let pinnedSites = this._filterPinnedSites(aSites, aCell);
+
+    // Correct pinned site positions.
+    pinnedSites.forEach(function (aSite) {
+      aSites[aSites.indexOf(aSite)] = aSites[aSite.cell.index];
+      aSites[aSite.cell.index] = aSite;
+    }, this);
+
+    // There might be a pinned cell that got pushed out of the grid, try to
+    // sneak it in by removing a lower-priority cell.
+    if (this._hasOverflowedPinnedSite(aSites, aCell))
+      this._repositionOverflowedPinnedSite(aSites, aCell);
+  },
+
+  /**
+   * Filter pinned sites out of the grid that are still on their old positions
+   * and have not moved.
+   * @param aSites The array of sites to filter.
+   * @param aCell The drop target cell.
+   * @return The filtered array of sites.
+   */
+  _filterPinnedSites: function DropPreview_filterPinnedSites(aSites, aCell) {
+    let draggedSite = gDrag.draggedSite;
+
+    // When dropping on a cell that contains a pinned site make sure that all
+    // pinned cells surrounding the drop target are moved as well.
+    let range = this._getPinnedRange(aCell);
+
+    return aSites.filter(function (aSite, aIndex) {
+      // The site must be valid, pinned and not the dragged site.
+      if (!aSite || aSite == draggedSite || !aSite.isPinned())
+        return false;
+
+      let index = aSite.cell.index;
+
+      // If it's not in the 'pinned range' it's a valid pinned site.
+      return (index > range.end || index < range.start);
+    });
+  },
+
+  /**
+   * Determines the range of pinned sites surrounding the drop target cell.
+   * @param aCell The drop target cell.
+   * @return The range of pinned cells.
+   */
+  _getPinnedRange: function DropPreview_getPinnedRange(aCell) {
+    let dropIndex = aCell.index;
+    let range = {start: dropIndex, end: dropIndex};
+
+    // We need a pinned range only when dropping on a pinned site.
+    if (aCell.containsPinnedSite()) {
+      let links = gPinnedLinks.links;
+
+      // Find all previous siblings of the drop target that are pinned as well.
+      while (range.start && links[range.start - 1])
+        range.start--;
+
+      let maxEnd = links.length - 1;
+
+      // Find all next siblings of the drop target that are pinned as well.
+      while (range.end < maxEnd && links[range.end + 1])
+        range.end++;
+    }
+
+    return range;
+  },
+
+  /**
+   * Checks if the given array of sites contains a pinned site that has
+   * been pushed out of the grid.
+   * @param aSites The array of sites to check.
+   * @param aCell The drop target cell.
+   * @return Whether there is an overflowed pinned cell.
+   */
+  _hasOverflowedPinnedSite:
+    function DropPreview_hasOverflowedPinnedSite(aSites, aCell) {
+
+    // If the drop target isn't pinned there's no way a pinned site has been
+    // pushed out of the grid so we can just exit here.
+    if (!aCell.containsPinnedSite())
+      return false;
+
+    let cells = gGrid.cells;
+
+    // No cells have been pushed out of the grid, nothing to do here.
+    if (aSites.length <= cells.length)
+      return false;
+
+    let overflowedSite = aSites[cells.length];
+
+    // Nothing to do if the site that got pushed out of the grid is not pinned.
+    return (overflowedSite && overflowedSite.isPinned());
+  },
+
+  /**
+   * We have a overflowed pinned site that we need to re-position so that it's
+   * visible again. We try to find a lower-priority cell (empty or containing
+   * an unpinned site) that we can move it to.
+   * @param aSites The array of sites.
+   * @param aCell The drop target cell.
+   */
+  _repositionOverflowedPinnedSite:
+    function DropPreview_repositionOverflowedPinnedSite(aSites, aCell) {
+
+    // Try to find a lower-priority cell (empty or containing an unpinned site).
+    let index = this._indexOfLowerPrioritySite(aSites, aCell);
+
+    if (index > -1) {
+      let cells = gGrid.cells;
+      let dropIndex = aCell.index;
+
+      // Move all pinned cells to their new positions to let the overflowed
+      // site fit into the grid.
+      for (let i = index + 1, lastPosition = index; i < aSites.length; i++) {
+        if (i != dropIndex) {
+          aSites[lastPosition] = aSites[i];
+          lastPosition = i;
+        }
+      }
+
+      // Finally, remove the overflowed site from its previous position.
+      aSites.splice(cells.length, 1);
+    }
+  },
+
+  /**
+   * Finds the index of the last cell that is empty or contains an unpinned
+   * site. These are considered to be of a lower priority.
+   * @param aSites The array of sites.
+   * @param aCell The drop target cell.
+   * @return The cell's index.
+   */
+  _indexOfLowerPrioritySite:
+    function DropPreview_indexOfLowerPrioritySite(aSites, aCell) {
+
+    let cells = gGrid.cells;
+    let dropIndex = aCell.index;
+
+    // Search (beginning with the last site in the grid) for a site that is
+    // empty or unpinned (an thus lower-priority) and can be pushed out of the
+    // grid instead of the pinned site.
+    for (let i = cells.length - 1; i >= 0; i--) {
+      // The cell that is our drop target is not a good choice.
+      if (i == dropIndex)
+        continue;
+
+      let site = aSites[i];
+
+      // We can use the cell only if it's empty or the site is un-pinned.
+      if (!site || !site.isPinned())
+        return i;
+    }
+
+    return -1;
+  }
+};