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

This is a reland of fa8a5d39

Original change's description:
> 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/1345709
> Reviewed-by: calamity <calamity@chromium.org>
> Commit-Queue: Sam McNally <sammc@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#610019}

Bug: 708299
Tbr: calamity@chromium.org
Change-Id: I4de9726b919f88a1efe98f036687de07b23715c2
Reviewed-on: https://chromium-review.googlesource.com/c/1347630Reviewed-by: Sam McNally <sammc@chromium.org>
Commit-Queue: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610358}

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();