Extensions: fix label color.

Bug: 867005
Change-Id: Ie56bf0c098bd625a506395cb3ea77eb3f38f18ef
Reviewed-on: https://chromium-review.googlesource.com/1148764Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Scott Chen <scottchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577777}

chrome/browser/resources/md_extensions/item_list.html

@@ -53,7 +53,7 @@
       }
 
       #app-title {
-        @apply --cr-section-text;
+        color: var(--cr-primary-text-color);
         font-size: 123%;
         font-weight: 400;
         letter-spacing: .25px;