Implement single-selection mode for SelectionDelegate.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/widget/selection/SelectionDelegate.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/widget/selection/SelectionDelegate.java b/chrome/android/java/src/org/chromium/chrome/browser/widget/selection/SelectionDelegate.java
index d718fc7c2822c9714275a5fb6025701ed60e5838..03f0b031f5be7f12da1a7da1bd469ebb72abe8d4 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/widget/selection/SelectionDelegate.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/widget/selection/SelectionDelegate.java
@@ -16,6 +16,8 @@ import java.util.Set;
  * @param <E> The type of the selectable items this delegate interacts with.
  */
 public class SelectionDelegate<E> {
+    // True if the SelectionDelegate should only support a single item being selected at a time.
+    private boolean mIsSingleSelection;
 
     /**
      * Observer interface to be notified of selection changes.
@@ -26,20 +28,31 @@ public class SelectionDelegate<E> {
          * @param selectedItems The list of currently selected items. An empty list indicates there
          *                      is no selection.
          */
-        public void onSelectionStateChange(List<E> selectedItems);
+        void onSelectionStateChange(List<E> selectedItems);
     }
 
     private Set<E> mSelectedItems = new HashSet<>();
     private ObserverList<SelectionObserver<E>> mObservers = new ObserverList<>();
 
     /**
+     * Sets the mode of this SelectionDelegate to single-selection.
+     */
+    public void setSingleSelectionMode() {
+        mIsSingleSelection = true;
+    }
+
+    /**
      * Toggles the selected state for the given item.
      * @param item The item to toggle.
      * @return Whether the item is selected.
      */
     public boolean toggleSelectionForItem(E item) {
-        if (mSelectedItems.contains(item)) mSelectedItems.remove(item);
-        else mSelectedItems.add(item);
+        if (mSelectedItems.contains(item)) {
+            mSelectedItems.remove(item);
+        } else {
+            if (mIsSingleSelection) mSelectedItems.clear();
+            mSelectedItems.add(item);
+        }
 
         notifyObservers();
 
@@ -99,5 +112,4 @@ public class SelectionDelegate<E> {
             observer.onSelectionStateChange(selectedItems);
         }
     }
-
 }