[Downloads UI] Fix selection toggle for updated items

When a download item is updated, its toggle state should carry over
from the previous DownloadHistoryItemWrapper. This fixes a bug
where a selection remained established if it the Download UI was
opened in two windows and a selected item in one window was
removed from the other window.

Also fixes some variable naming in SelectionDelegate.java

BUG=648938

Review-Url: https://codereview.chromium.org/2361163004
Cr-Commit-Position: refs/heads/master@{#420788}

chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadHistoryAdapter.java

@@ -206,6 +206,12 @@ public class DownloadHistoryAdapter extends DateDividedAdapter implements Downlo
             list.add(wrapper);
             mFilePathsToItemsMap.addItem(wrapper);
         } else {
+            DownloadItemWrapper previousWrapper = list.get(index);
+            // If the previous item was selected, the updated item should be selected as well.
+            if (getSelectionDelegate().isItemSelected(previousWrapper)) {
+                getSelectionDelegate().toggleSelectionForItem(previousWrapper);
+                getSelectionDelegate().toggleSelectionForItem(wrapper);
+            }
             // Update the old one.
             list.set(index, wrapper);
             mFilePathsToItemsMap.replaceItem(wrapper);

chrome/android/java/src/org/chromium/chrome/browser/widget/selection/SelectionDelegate.java

@@ -34,25 +34,25 @@ public class SelectionDelegate<E> {
 
     /**
      * Toggles the selected state for the given item.
-     * @param itemId The id of the item to toggle.
+     * @param item The item to toggle.
      * @return Whether the item is selected.
      */
-    public boolean toggleSelectionForItem(E itemId) {
-        if (mSelectedItems.contains(itemId)) mSelectedItems.remove(itemId);
-        else mSelectedItems.add(itemId);
+    public boolean toggleSelectionForItem(E item) {
+        if (mSelectedItems.contains(item)) mSelectedItems.remove(item);
+        else mSelectedItems.add(item);
 
         notifyObservers();
 
-        return isItemSelected(itemId);
+        return isItemSelected(item);
     }
 
     /**
-     * True if the bookmark is selected. False otherwise.
-     * @param itemId The id of the item.
+     * True if the item is selected. False otherwise.
+     * @param item The item.
      * @return Whether the item is selected.
      */
-    public boolean isItemSelected(E itemId) {
-        return mSelectedItems.contains(itemId);
+    public boolean isItemSelected(E item) {
+        return mSelectedItems.contains(item);
     }
 
     /**