Delegating the "are images allowed" decision to renderer.

chrome/common/extensions/api/extension_api.json

 [
   {
     "namespace": "extension",
     "unprivileged": true,
     "types": [
       {
         "id": "MessageSender",
         "type": "object",
         "description": "An object containing information about the script context that sent a message or request.",
         "properties": {
@@ skipping 8362 matching lines @@
       "cookies": {
         "$ref": "ContentSetting",
         "description": "Whether to allow cookies and other local data to be set by websites. One of<br><var>allow</var>: Accept cookies,<br><var>block</var>: Block cookies,<br><var>session_only</var>: Accept cookies only for the current session. <br>Default is <var>allow</var>.<br>The primary URL is the URL representing the cookie origin. The secondary URL is the URL of the top-level frame.",
         "value": [
           "cookies",
           {"type":"string", "enum": ["allow", "block", "session_only"]}
         ]
       },
       "images": {
         "$ref": "ContentSetting",
-        "description": "Whether to show images. One of<br><var>allow</var>: Show images,<br><var>block</var>: Don't show images. <br>Default is <var>allow</var>.<br>The primary URL is the main-frame URL. The secondary URL is not used.",
+        "description": "Whether to show images. One of<br><var>allow</var>: Show images,<br><var>block</var>: Don't show images. <br>Default is <var>allow</var>.<br>The primary URL is the main-frame URL. The secondary URL is the URL of the image.",
         "value": [
           "images",
           {"type":"string", "enum": ["allow", "block"]}
         ]
       },
       "javascript": {
         "$ref": "ContentSetting",
         "description": "Whether to run JavaScript. One of<br><var>allow</var>: Run JavaScript,<br><var>block</var>: Don't run JavaScript. <br>Default is <var>allow</var>.<br>The primary URL is the main-frame URL. The secondary URL is not used.",
         "value": [
           "javascript",
@@ skipping 772 matching lines @@
                   }
                 }
               }
             ]
           }
         ]
       }
     ]
   }
 ]