Fix mixed content autoupgrades pref logic

The pref used for the EnableStricterMixedContentTreatment enterprise
policy had its logic accidentally inverted as part of a refactor in
crrev.com/c/2151841. This inverts the logic back.

Bug: 1091033
Change-Id: Id14e89a304514b923cabecf6c4da982b0f60924d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2229241
Auto-Submit: Carlos IL <carlosil@chromium.org>
Reviewed-by: Balazs Engedy <engedy@chromium.org>
Commit-Queue: Carlos IL <carlosil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#775761}

components/content_settings/browser/tab_specific_content_settings.cc

@@ -749,7 +749,7 @@ void TabSpecificContentSettings::ReadyToCommitNavigation(
 
   PrefService* prefs = delegate_->GetPrefs();
   if (prefs &&
-      prefs->GetBoolean(
+      !prefs->GetBoolean(
           security_state::prefs::kStricterMixedContentTreatmentEnabled)) {
     auto* render_frame_host = navigation_handle->GetRenderFrameHost();
     mojo::AssociatedRemote<content_settings::mojom::ContentSettingsAgent>