MD History: Delete button in the toolbar allows deletion of multiple history-items.

chrome/browser/resources/md_history/history_card_manager.js

Index: chrome/browser/resources/md_history/history_card_manager.js
diff --git a/chrome/browser/resources/md_history/history_card_manager.js b/chrome/browser/resources/md_history/history_card_manager.js
index 6f9cae24671a0f2ac9b27d3a60f208f0c4db943e..20f4d7f970aaf3cb8d22cf2c4fb56ff70bab7dbd 100644
--- a/chrome/browser/resources/md_history/history_card_manager.js
+++ b/chrome/browser/resources/md_history/history_card_manager.js
@@ -100,6 +100,7 @@ Polymer({
   /**
    * Cycle through each entry in historyDataByDay_ and set all items to be
    * unselected.
+   * @param {number} overallItemCount The number of items selected.
    */
   unselectAllItems: function(overallItemCount) {
     var historyCardData = this.historyDataByDay_;
@@ -112,13 +113,58 @@ Polymer({
               '.selected', false);
           overallItemCount--;
           if (overallItemCount == 0)
-            break;
+            return;
         }
       }
     }
   },
 
   /**
+   * Remove all selected items from the overall array so that they are also
+   * removed from view. Make sure that the card length and positioning is
+   * updated accordingly.
+   * @param {number} overallItemCount The number of items selected.
+   */
+  removeDeletedHistory: function(overallItemCount) {
+    for (var i = 0; i < this.historyDataByDay_.length; i++) {
+      var items = this.historyDataByDay_[i].historyItems;
+      var itemDeletedFromCard = false;
+
+      for (var j = items.length - 1; j >= 0; j--) {

[tsergeant, 2016/01/25 01:43:14]

There's a problem here that is kinda tough to explain.

When you delete an item, the historyDataByDay[i].historyItems loses an item and
gets smaller.

Specifically, the item which used to be at position `j` is removed. The item
which used to be at position `j+1` will then move back to position `j`.

You'll continue looping, and move on to the item in position `j+1`, but *that*
item, in turn, used to be in position `j+2`. You will have completely skipped
over the item that used to at `j+1` and is now at `j`.

You can avoid this by decrementing j after you delete anything.

[hsampson, 2016/01/25 04:15:42]

As discussed the loop going through backwards is to account for this.

+        if (items[j].selected) {
+          this.splice('historyDataByDay_.' + i + '.historyItems', j, 1);
+          itemDeletedFromCard = true;
+          overallItemCount--;
+          if (overallItemCount == 0) {
+            this.removeEmptyCards_();
+            // If the last card has been removed don't try to update its size.
+            if (this.historyDataByDay_.length > i) {

[tsergeant, 2016/01/25 01:43:14]

Remove {}

[hsampson, 2016/01/25 04:15:42]

Done.

+              this.$['infinite-list'].updateSizeForItem(i);
+            }
+            return;
+          }
+        }
+      }
+      if (itemDeletedFromCard)
+        this.$['infinite-list'].updateSizeForItem(i);
+    }
+  },
+
+  /**
+   * If a given day has had all the history it contains removed, remove this
+   * day from the array.
+   * @private
+   */
+  removeEmptyCards_: function() {
+    var historyCards = this.historyDataByDay_;
+    for (var i = historyCards.length - 1; i > -1; i--) {
+      if (historyCards[i].historyItems.length == 0) {
+        this.splice('historyDataByDay_', i, 1);
+      }
+    }
+  },
+
+  /**
    * Adds the given items into historyDataByDay_. Adds items to the last
    * existing day if the date matches, creates a new element otherwise.
    * @param {string} date The date of the history items.
@@ -140,6 +186,33 @@ Polymer({
   },
 
   /**
+   * Based on which items are selected, collect an array of the info required
+   * for chrome.send('removeHistory', ...).
+   * @param {number} count The number of items that are selected.
+   * @return {array} toBeRemoved An array of objects which contain information
+   * on which history-items should be deleted.
+   */
+  getItemsToDelete: function(count) {
+    var toBeRemoved = [];
+    for (var i = 0; i < this.historyDataByDay_.length; i++) {
+      var items = this.historyDataByDay_[i].historyItems;
+      for (j = 0; j < items.length; j++) {
+        if (items[j].selected) {
+
+          toBeRemoved.push({
+            url: items[j].url,
+            timestamps: items[j].allTimestamps
+          });
+
+          count--;
+          if (count == 0)
+            return toBeRemoved;
+        }
+      }
+    }
+  },
+
+  /**
    * Called when the card manager is scrolled.
    * @private
    */