Add CC dark theme option

This commit adds an option to enable a dark theme in the Community
Console. It can be enabled manually with a switch which is injected in
the CC or automatically by syncing it with the OS dark mode setting.

Change-Id: I7506e80a409c5b0190d942c9de88354b6c0cce10
diff --git a/src/content_scripts/console_inject_start.js b/src/content_scripts/console_inject_start.js
index 92ad72b..52482c5 100644
--- a/src/content_scripts/console_inject_start.js
+++ b/src/content_scripts/console_inject_start.js
@@ -10,4 +10,19 @@
     document.querySelector('html').setAttribute(
         'data-startup', JSON.stringify(startup));
   }
+
+  if (items.ccdarktheme) {
+    switch (items.ccdarktheme_mode) {
+      case 'switch':
+        if (items.ccdarktheme_switch_status == true)
+          injectStylesheet(chrome.runtime.getURL('injections/ccdarktheme.css'));
+        break;
+
+      case 'system':
+        injectStylesheet(chrome.runtime.getURL('injections/ccdarktheme.css'), {
+          'media': '(prefers-color-scheme: dark)',
+        });
+        break;
+    }
+  }
 });