Add new danger type for uncommon or unknown downloads.

chrome/common/extensions/api/experimental.downloads.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": "experimental.downloads",
     "events": [
       {
         "name": "onCreated",
@@ skipping 59 matching lines @@
         "nodoc": "true",
         "value": "url",
         "description": "The download's URL is malicious."
       },
       "DANGER_CONTENT": {
         "type": "string",
         "nodoc": "true",
         "value": "content",
         "description": "The download's content is malicious."
       },
+      "DANGER_UNCOMMON": {
+        "type": "string",
+        "value": "uncommon",
+        "description": "The download is not commonly downloaded and could be dangerous."
+      },
       "ERROR_GENERIC": {
         "type": "string",
         "value": "I'm afraid I can't do that.",
         "description": "Generic error."
       },
       "ERROR_INVALID_URL": {
         "type": "string",
         "value": "Invalid URL.",
         "description": "The URL was invalid."
       },
@@ skipping 17 matching lines @@
             "binaryValue": {
               "type": "array",
               "optional": true,
               "description": "Value of the HTTP header if it cannot be represented by UTF-8, stored as individual byte values (0..255).",
               "items": {"type": "integer"}
             }
           }
         }
       },
       {
+        "id": "DownloadDangerType",
+        "description": "String indicating whether a download is known to be safe or is considered dangerous. The values correspond to the <code>DANGER_SAFE</code>, <code>DANGER_FILE</code>, <code>DANGER_URL</code>, <code>DANGER_CONTENT</code>, and <code>DANGER_UNCOMMON</code> properties.",
+        "type": "string",
+        "enum": ["safe", "file", "url", "content", "uncommon"]
+      },
+      {
         "id": "DownloadItem",
         "type": "object",
         "nodoc": "true",
         "description": "The state of a file as it is downloaded from the internet.",
         "properties": {
           "id": {
             "type": "integer",
             "description": "An identifier that is persistent across browser sessions."
           },
           "url": {
             "type": "string",
             "description": "absolute URL"
           },
           "filename": {
             "type": "string",
             "description": "absolute local path"
           },
           "danger": {
-            "type": "string",
+            "$ref": "DownloadDangerType",
             "description": "Indication of whether this download is thought to be safe or known to be suspicious.",
-            "enum": ["safe", "file", "url", "content"],
             "optional": true
           },
           "dangerAccepted": {
             "type": "boolean",
             "description": "true if the user has accepted the download's danger.",
             "optional": true
           },
           "mime": {
             "type": "string",
             "description": "The file's MIME type."
@@ skipping 105 matching lines @@
             "type": "string",
             "optional": true,
             "description": "absolute URL"
           },
           "filename": {
             "type": "string",
             "optional": true,
             "description": "absolute local path"
           },
           "danger": {
-            "type": "string",
+            "$ref": "DownloadDangerType",
             "description": "Indication of whether this download is thought to be safe or known to be suspicious.",
-            "enum": ["safe", "file", "url"],
             "optional": true
           },
           "dangerAccepted": {
             "type": "boolean",
             "optional": true,
             "description": "true if the user has accepted the download's danger."
           },
           "mime": {
             "type": "string",
             "optional": true,
@@ skipping 367 matching lines @@
                 "type": "string",
                 "description": "A URL to an image that represents the download. If a file icon cannot be determined, chrome.extension.lastError will contain an error message."
               }
             ]
           }
         ]
       }
     ]
   }
 ]