Site Settings Desktop: Minor fix.

Use preprocess=true instead of flattenhtml and allowexternalscript.

BUG=635850
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2344203002
Cr-Commit-Position: refs/heads/master@{#419429}

chrome/browser/resources/settings/settings_resources.grd

@@ -772,8 +772,7 @@
       <structure name="IDR_SETTINGS_SITE_SETTINGS_CATEGORY_HTML"
                  file="site_settings/site_settings_category.html"
                  type="chrome_html"
-                 flattenhtml="true"
-                 allowexternalscript="true" />
+                 preprocess="true" />
       <structure name="IDR_SETTINGS_SITE_SETTINGS_CATEGORY_JS"
                  file="site_settings/site_settings_category.js"
                  type="chrome_html" />