[MD History] Add keyboard navigation to the main history list.

chrome/browser/resources/md_history/history_list.html

Index: chrome/browser/resources/md_history/history_list.html
diff --git a/chrome/browser/resources/md_history/history_list.html b/chrome/browser/resources/md_history/history_list.html
index fe68b5466923a603a7b2b8c3cf82d88676cc4486..ef20bf5165d1c64d402aa23fa97ae9304cae16d3 100644
--- a/chrome/browser/resources/md_history/history_list.html
+++ b/chrome/browser/resources/md_history/history_list.html
@@ -25,7 +25,8 @@
     <iron-list items="{{historyData_}}" as="item" id="infinite-list"
         hidden$="[[!hasResults(historyData_.length)]]">
       <template>
-        <history-item item="[[item]]"
+        <history-item tabindex="-1"
+            item="[[item]]"
             selected="{{item.selected}}"
             is-first-item="[[isFirstItem_(index)]]"
             is-card-start="[[isCardStart_(item, index, historyData_.length)]]"
@@ -34,7 +35,9 @@
             search-term="[[searchedTerm]]"
             number-of-items="[[historyData_.length]]"
             path="[[pathForItem_(index)]]"
-            index="[[index]]">
+            index="[[index]]"
+            tab-index="[[tabIndex]]"

[Dan Beam, 2016/09/15 16:51:10]

can we just name this something else?  iron-list-tab-index?

this might invoke HTMLElement#tabIndex, which is a DOM 0 accessor
semi-equivalent to setAttribute('tabindex', ...)

+            last-focused="{{lastFocused_}}">
         </history-item>
       </template>
     </iron-list>