Fix selection jumping around when removing multiple items in cr-list.

Previously, when the selected item is removed, the selection is changed
to the index after where the old lead index was. When multiple items are
removed, the logical next item may move multiple positions. Avoid this
by moving to the item that hasn't been removed from prior to the
permutation - using its position after the permutation.

Bug: 708299
Change-Id: I9393c9f00d5453ef3c3d5378758bb63ed29c43b7
Reviewed-on: https://chromium-review.googlesource.com/c/1345709Reviewed-by: calamity <calamity@chromium.org>
Commit-Queue: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610019}

chrome/test/data/webui/list_selection_model_test.html

@@ -157,8 +157,8 @@ function testAdjust12() {
 
   adjust(sm, 5, 20, 10);
 
-  assertEquals(-1, sm.leadIndex, 'lead');
-  assertEquals(-1, sm.anchorIndex, 'anchor');
+  assertEquals(0, sm.leadIndex, 'lead');
+  assertEquals(0, sm.anchorIndex, 'anchor');
   assertArrayEquals(range(0, 4), sm.selectedIndexes);
 }
 
@@ -175,6 +175,64 @@ function testAdjust13() {
   assertArrayEquals(range(0, 14), sm.selectedIndexes);
 }
 
+function testAdjust14() {
+  var sm = createSelectionModel(5, true);
+
+  sm.selectedIndexes = [2, 3];
+  sm.leadIndex = sm.anchorIndex = 3;
+
+  adjust(sm, 2, 2, 0);
+
+  assertEquals(2, sm.leadIndex, 'lead');
+  assertEquals(2, sm.anchorIndex, 'anchor');
+  assertArrayEquals(range(2, 2), sm.selectedIndexes);
+}
+
+function testAdjust15() {
+  var sm = createSelectionModel(7, true);
+
+  sm.selectedIndexes = [1, 3, 5];
+  sm.leadIndex = sm.anchorIndex = 1;
+
+  adjust(sm, 1, 1, 0);
+  adjust(sm, 2, 1, 0);
+  adjust(sm, 3, 1, 0);
+
+  assertEquals(3, sm.leadIndex, 'lead');
+  assertEquals(3, sm.anchorIndex, 'anchor');
+  assertArrayEquals(range(3, 3), sm.selectedIndexes);
+}
+
+function testAdjust16() {
+  var sm = createSelectionModel(7, true);
+
+  sm.selectedIndexes = [1, 3, 5];
+  sm.leadIndex = sm.anchorIndex = 3;
+
+  adjust(sm, 1, 1, 0);
+  adjust(sm, 2, 1, 0);
+  adjust(sm, 3, 1, 0);
+
+  assertEquals(3, sm.leadIndex, 'lead');
+  assertEquals(3, sm.anchorIndex, 'anchor');
+  assertArrayEquals(range(3, 3), sm.selectedIndexes);
+}
+
+function testAdjust17() {
+  var sm = createSelectionModel(7, true);
+
+  sm.selectedIndexes = [1, 3, 5];
+  sm.leadIndex = sm.anchorIndex = 5;
+
+  adjust(sm, 1, 1, 0);
+  adjust(sm, 2, 1, 0);
+  adjust(sm, 3, 1, 0);
+
+  assertEquals(3, sm.leadIndex, 'lead');
+  assertEquals(3, sm.anchorIndex, 'anchor');
+  assertArrayEquals(range(3, 3), sm.selectedIndexes);
+}
+
 function testLeadAndAnchor1() {
   var sm = createSelectionModel(20, true);
 
@@ -191,8 +249,8 @@ function testLeadAndAnchor2() {
   sm.leadIndex = sm.anchorIndex = 10;
   sm.selectAll();
 
-  assertEquals(-1, sm.leadIndex, 'lead');
-  assertEquals(-1, sm.anchorIndex, 'anchor');
+  assertEquals(0, sm.leadIndex, 'lead');
+  assertEquals(0, sm.anchorIndex, 'anchor');
 }
 
 function testSelectAll() {

ui/webui/resources/js/cr/ui/list_selection_model.js

@@ -105,8 +105,14 @@ cr.define('cr.ui', function() {
      * @private
      */
     getNearestSelectedIndex_: function(index) {
-      if (index == -1)
+      if (index == -1) {
+        // If no index is provided, pick the first selected index if there is
+        // one.
+        if (this.selectedIndexes.length) {
+          return this.selectedIndexes[0];
+        }
         return -1;
+      }
 
       var result = Infinity;
       for (var i in this.selectedIndexes_) {
@@ -348,8 +354,15 @@ cr.define('cr.ui', function() {
       if (oldSelectedItemsCount && !this.selectedIndexes.length &&
           this.length_ && oldLeadIndex != -1) {
         // All selected items are deleted. We move selection to next item of
-        // last selected item.
-        this.selectedIndexes = [Math.min(oldLeadIndex, this.length_ - 1)];
+        // last selected item, following it to its new position.
+        let newSelectedIndex = Math.min(oldLeadIndex, this.length_ - 1);
+        for (let i = oldLeadIndex + 1; i < permutation.length; ++i) {
+          if (permutation[i] != -1) {
+            newSelectedIndex = permutation[i];
+            break;
+          }
+        }
+        this.selectedIndexes = [newSelectedIndex];
       }
 
       this.endChange();