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..cec3ee2e279c6a6d550757c8657a4aea6d7281c6 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.

[calamity, 2016/01/21 00:11:08]

nit: Capitalize 'The' since it's the start of the description. (repeat
elsewhere)

[hsampson, 2016/01/21 05:34:47]

Done.

    */
   unselectAllItems: function(overallItemCount) {
     var historyCardData = this.historyDataByDay_;
@@ -112,13 +113,60 @@ 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) {
+    var itemDeletedFromCard = false;
+
+    for (var i = 0; i < this.historyDataByDay_.length; i++) {
+      var items = this.historyDataByDay_[i].historyItems;
+
+      for (var j = items.length - 1; j > -1; j--) {

[calamity, 2016/01/21 00:11:08]

j >= 0 tends to be the usual way to do this.

[hsampson, 2016/01/21 05:34:46]

Done.

+        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) {
+              this.$['infinite-list'].updateSizeForItem(i);
+            }
+            return;
+          }
+        }
+      }
+      if (itemDeletedFromCard)
+        this.$['infinite-list'].updateSizeForItem(i);
+      itemDeletedFromCard = false;

[calamity, 2016/01/21 00:11:08]

Instead of doing this, just move the declaration of itemDeletedFromCard inside
the first for loop.

[hsampson, 2016/01/21 05:34:46]

Done.

+    }
+  },
+
+  /**
+   * 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 +188,34 @@ 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) {

[calamity, 2016/01/21 00:11:08]

After a small chat with Tim, I think there's a possibility of improving the
processing.

So the code is often looping through the entirety of history data in order to
find selected things. My idea was to pass more information in the notification
so that we could have history-card-manager track all selected items and just
have enough information there to do what we need.

I think this change is moderately complex and you would need to account for
changing indexes when deleting items. It's a fun data flow/structure and code
design problem though.

tl;dr: it would be nice to have a history-card-manager.selectedItems array

It's up to you whether you want to do this now/later/ever. Feel free to grab me
for a chat if you are having the big confuse.

[hsampson, 2016/01/21 05:34:46]

Once all of the big cls are uploaded I will create a separate cl to deal with
this.

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

Chris and I have ~even more~ ideas about how to do this. Let's chat about it
when CLs start clearing up.

+    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)
+            break;

[calamity, 2016/01/21 00:11:08]

Change this to return toBeRemoved;

[hsampson, 2016/01/21 05:34:46]

Done.

+        }
+      }
+    }
+    return toBeRemoved;
+  },
+
+  /**
    * Called when the card manager is scrolled.
    * @private
    */