[MD History] Add shift-selection to the history lists.

chrome/browser/resources/md_history/history_item.js

Index: chrome/browser/resources/md_history/history_item.js
diff --git a/chrome/browser/resources/md_history/history_item.js b/chrome/browser/resources/md_history/history_item.js
index 4e4adf9ed2bb0f0c447a058ff95d47cc4735fce4..b6b6603dfd28f920c4b07f74edfe8b5a1e6d983c 100644
--- a/chrome/browser/resources/md_history/history_item.js
+++ b/chrome/browser/resources/md_history/history_item.js
@@ -37,14 +37,26 @@ cr.define('md_history', function() {
     /**
      * When a history-item is selected the toolbar is notified and increases
      * or decreases its count of selected items accordingly.
+     * @param {MouseEvent} e
      * @private
      */
-    onCheckboxSelected_: function() {
+    onCheckboxSelected_: function(e) {
       // TODO(calamity): Fire this event whenever |selected| changes.
       this.fire('history-checkbox-select', {
         element: this,
-        countAddition: this.$.checkbox.checked ? 1 : -1
+        shiftKey: e.shiftKey,
       });
+      e.preventDefault();
+    },
+
+    /**
+     * @param {MouseEvent} e
+     * @private
+     */
+    onCheckboxMousedown_: function(e) {
+      // Prevent shift clicking a checkbox from selecting text.
+      if (e.shiftKey)
+        e.preventDefault();
     },
 
     /**