Support also excluding content types in declarative webrequest conditions.

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

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var onRequest = chrome.declarativeWebRequest.onRequest;
 var AddResponseHeader =
     chrome.declarativeWebRequest.AddResponseHeader;
 var RequestMatcher = chrome.declarativeWebRequest.RequestMatcher;
 var CancelRequest = chrome.declarativeWebRequest.CancelRequest;
 var RedirectByRegEx = chrome.declarativeWebRequest.RedirectByRegEx;
@@ skipping 86 matching lines @@
       [ ["onErrorOccurred"] ]);
     onRequest.addRules(
       [ {'conditions': [
            new RequestMatcher({
              'url': {
                  'pathSuffix': ".html",
                  'ports': [testServerPort, [1000, 2000]],
                  'schemes': ["http"]
              },
              'resourceType': ["main_frame"],
-             'contentType': ["text/html"]})],
+             'contentType': ["text/html"],
+             'excludeContentType': ["image/png"]})],
          'actions': [new CancelRequest()]}
       ],
       function() {navigateAndWait(getURLHttpWithHeaders());}
     );
   },
 
   function testRedirectRequest() {
     ignoreUnexpected = true;
     expect(
       [
@@ skipping 349 matching lines @@
                   this.status + ", responseText: " + this.responseText);
             }
           }
           req.open("GET", getURLHttpXHRData(), asynchronous);
           req.send(null);
         });
       }
     );
   },
   ]);