Band selection: Add handling for layout changes.

Previously, the app would crash druing band selection after the layout had changed.

Change-Id: I51ed2908d30e16f4d77769c798dfcef5f1ee1602

packages/DocumentsUI/src/com/android/documentsui/DirectoryFragment.java

@@ -573,6 +573,9 @@ public class DirectoryFragment extends Fragment {
         }
 
         mRecView.setLayoutManager(layout);
+        // TODO: Once b/23691541 is resolved, use a listener within MultiSelectManager instead of
+        // imperatively calling this function.
+        mSelectionManager.handleLayoutChanged();
         // setting layout manager automatically invalidates existing ViewHolders.
         mThumbSize = new Point(thumbSize, thumbSize);
     }

packages/DocumentsUI/src/com/android/documentsui/MultiSelectManager.java

@@ -250,6 +250,10 @@ public final class MultiSelectManager {
         notifySelectionChanged();
     }
 
+    public void handleLayoutChanged() {
+        mBandSelectManager.handleLayoutChanged();
+    }
+
     /**
      * Clears the selection, without notifying anyone.
      */
@@ -1191,6 +1195,18 @@ public final class MultiSelectManager {
             mModel.addOnSelectionChangedListener(this);
         }
 
+        /**
+         * Handle a change in layout by cleaning up and getting rid of the old model and creating
+         * a new model which will track the new layout.
+         */
+        public void handleLayoutChanged() {
+            mModel.removeOnSelectionChangedListener(this);
+            mModel.stopListening();
+
+            mModel = new BandSelectModel((RuntimeRecyclerViewHelper) mHelper);
+            mModel.addOnSelectionChangedListener(this);
+        }
+
         /**
          * Processes a MotionEvent by starting, ending, or resizing the band select overlay.
          * @param e