MD Settings: make iron list offset so items render onscreen

R=dbeam@chromium.org
BUG=689356
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2805213003
Cr-Commit-Position: refs/heads/master@{#463312}

chrome/browser/resources/settings/search_engines_page/search_engines_list.html

@@ -46,7 +46,8 @@
       </div>
       <div id="container" class="scroll-container">
         <iron-list items="[[engines]]" scroll-target="[[scrollTarget]]"
-            class$="[[getIronListClass_(scrollTarget)]]">
+            class$="[[getIronListClass_(scrollTarget)]]"
+            scroll-offset="[[scrollOffset]]">
           <template>
             <settings-search-engine-entry engine="[[item]]"
                 tabindex$="[[tabIndex]]" iron-list-tab-index="[[tabIndex]]"

chrome/browser/resources/settings/search_engines_page/search_engines_list.js

@@ -25,6 +25,9 @@ Polymer({
       value: null,  // Required to populate class.
     },
 
+    /** Used to fix scrolling glitch when list is not top most element. */
+    scrollOffset: Number,
+
     /** @private {Object}*/
     lastFocused_: Object,
   },

chrome/browser/resources/settings/search_engines_page/search_engines_page.html

@@ -41,8 +41,8 @@
     <div id="noOtherEngines" hidden="[[otherEngines.length]]">
       $i18n{searchEnginesNoOtherEngines}
     </div>
-    <settings-search-engines-list engines="[[otherEngines]]" hide-headers
-          scroll-target="[[subpageScrollTarget]]">
+    <settings-search-engines-list id="otherEngines" engines="[[otherEngines]]"
+          hide-headers scroll-target="[[subpageScrollTarget]]">
     </settings-search-engines-list>
     <template is="dom-if" if="[[showExtensionsList_]]">
       <div class="settings-box first">

chrome/browser/resources/settings/search_engines_page/search_engines_page.js

@@ -59,6 +59,11 @@ Polymer({
         getSearchEnginesList().then(this.enginesChanged_.bind(this));
     this.addWebUIListener(
         'search-engines-changed', this.enginesChanged_.bind(this));
+
+    // Sets offset in iron-list that uses the page as a scrollTarget.
+    Polymer.RenderStatus.afterNextRender(this, function() {
+      this.$.otherEngines.scrollOffset = this.$.otherEngines.offsetTop;
+    });
   },
 
   /** @private */