Provide a small amount of padding in extension errors for the highlight border

Since extension errors are designed to take up the full amount of space, there
was no room left for the borders to indicate tab highlighting, and they were
slightly cut off. Fix this by adding a tiny bit of room above and below each
error, and to the end of the view details link.

Screenshots (after and before): http://imgur.com/acdRaXH,XDDIdZ8
BUG=380637

Review URL: https://codereview.chromium.org/599103004

Cr-Commit-Position: refs/heads/master@{#297092}

chrome/browser/resources/extensions/extension_error.css

@@ -45,9 +45,11 @@
 }
 
 .extension-error-metadata {
+  -webkit-padding-end: 1px;
   display: flex;
   flex-direction: row;
-  width: 100%;
+  margin-bottom: 1px;
+  margin-top: 1px;
 }
 
 .extension-error-icon {