Support also excluding content types in declarative webrequest conditions.

chrome/test/data/extensions/api_test/webrequest/test_declarative.js

Index: chrome/test/data/extensions/api_test/webrequest/test_declarative.js
diff --git a/chrome/test/data/extensions/api_test/webrequest/test_declarative.js b/chrome/test/data/extensions/api_test/webrequest/test_declarative.js
index 16bdf3fd82b60452a00ce99962f5261318e6c774..cb5ed24b6b42a68a472145b78f5c1e48fb5dd03a 100644
--- a/chrome/test/data/extensions/api_test/webrequest/test_declarative.js
+++ b/chrome/test/data/extensions/api_test/webrequest/test_declarative.js
@@ -104,7 +104,8 @@ runTests([
                  'schemes': ["http"]
              },
              'resourceType': ["main_frame"],
-             'contentType': ["text/html"]})],
+             'contentType': ["text/html"],
+             'excludeContentType': ["image/png"]})],
          'actions': [new CancelRequest()]}
       ],
       function() {navigateAndWait(getURLHttpWithHeaders());}