Actually compile the base/prefs code

chromiumcontent.gyp

@@ -4,6 +4,7 @@
       'target_name': 'chromiumcontent',
       'type': 'shared_library',
       'dependencies': [
+        '<(DEPTH)/base/base.gyp:base_prefs',
         '<(DEPTH)/content/content.gyp:content',
         '<(DEPTH)/content/content.gyp:content_shell_pak',
         'browser_net',