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..1e8afe05ab0ae4920eaa0cb740af7371d774b08b 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 mSingleSelection;
 
     /**
      * Observer interface to be notified of selection changes.
@@ -32,14 +34,25 @@ public class SelectionDelegate<E> {
     private Set<E> mSelectedItems = new HashSet<>();

[Michael van Ouwerkerk, 2017/04/04 13:54:31]

Should we document that E must have a meaningful equals() as SelectionDelegate
relies on that by putting it in a HashSet?

[Finnur, 2017/04/04 16:13:35]

Ditto.

     private ObserverList<SelectionObserver<E>> mObservers = new ObserverList<>();
 
+    /*

[Michael van Ouwerkerk, 2017/04/04 13:54:31]

nit: /** for JavaDoc

[Finnur, 2017/04/04 16:13:35]

Done.

+     * Sets the mode of this SelectionDelegate to single-selection.
+     */
+    public void setSingleSelectionMode() {
+        mSingleSelection = 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 (mSingleSelection) mSelectedItems.clear();
+            mSelectedItems.add(item);
+        }
 
         notifyObservers();
 
@@ -99,5 +112,4 @@ public class SelectionDelegate<E> {
             observer.onSelectionStateChange(selectedItems);
         }
     }
-
 }