MD Extensions: add test for empty description

Bug: 789895
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: If3b116a3ea86bd4c1f27ea97f3704a9fd3f00e64
Reviewed-on: https://chromium-review.googlesource.com/846286Reviewed-by: Dave Schuyler <dschuyler@chromium.org>
Commit-Queue: Scott Chen <scottchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526568}

chrome/browser/resources/md_extensions/detail_view.html

@@ -182,8 +182,8 @@
       }
 
       #size {
-        display: flex;
         align-items: center;
+        display: flex;
       }
 
       paper-spinner-lite {
@@ -268,7 +268,7 @@
         </div>
         <div class="section continuation block">
           <div class="section-title">$i18n{itemDescriptionLabel}</div>
-          <div class="section-content">
+          <div class="section-content" id="description">
             [[getDescription_(data.description, '$i18nPolymer{noDescription}')]]
           </div>
         </div>

chrome/test/data/webui/extensions/extension_detail_view_test.js

@@ -58,6 +58,9 @@ cr.define('extension_detail_view_tests', function() {
       expectTrue(testIsVisible('#icon'));
       expectTrue(testIsVisible('#enable-toggle'));
       expectFalse(testIsVisible('#extensions-options'));
+      expectTrue(
+          item.$.description.textContent.indexOf('This is an extension') !==
+          -1);
 
       // Check the checkboxes visibility and state. They should be visible
       // only if the associated option is enabled, and checked if the