Support also excluding content types in declarative webrequest conditions.

chrome/common/extensions/api/declarative_web_request.json

 // 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.
 
 [
   {
     "namespace": "declarativeWebRequest",
     "documentation_permissions_required": ["declarative", "declarativeWebRequest"],
     "types": [
       {
@@ skipping 11 matching lines @@
             "optional": true,
             "description": "Matches if the request type of a request is contained in the list. Requests that cannot match any of the types will be filtered out.",
             "items": { "type": "string", "enum": ["main_frame", "sub_frame", "stylesheet", "script", "image", "object", "xmlhttprequest", "other"] }
           },
           "contentType": {
             "type": "array",
             "optional": true,
             "description": "Matches if the MIME media type of a response (from the HTTP Content-Type header) is contained in the list.",
             "items": { "type": "string" }
           },
+          "excludeContentType": {
+            "type": "array",
+            "optional": true,
+            "description": "Matches if the MIME media type of a response (from the HTTP Content-Type header) is <em>not</em> contained in the list.",
+            "items": { "type": "string" }
+          },
           "instanceType": {
             "type": "string", "enum": ["declarativeWebRequest.RequestMatcher"],
             "nodoc": true
           }
         }
       },
       {
         "id": "CancelRequest",
         "description": "Declarative event action that cancels a network request.",
         "type": "object",
@@ skipping 333 matching lines @@
             "declarativeWebRequest.RemoveRequestHeader",
             "declarativeWebRequest.RemoveResponseHeader",
             "declarativeWebRequest.SetRequestHeader",
             "declarativeWebRequest.IgnoreRules"
           ]
         }
       }
     ]
   }
 ]