<webview> Implement clear http cache API.

extensions/common/api/web_view_internal.json

 // Copyright 2014 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": "webViewInternal",
     "description": "none",
     "compiler_options": {
       "implemented_in": "extensions/browser/api/guest_view/web_view/web_view_internal_api.h"
@@ skipping 26 matching lines @@
           },
           "localStorage": {
             "type": "boolean",
             "optional": true,
             "description": "Websites' local storage data."
           },
           "webSQL": {
             "type": "boolean",
             "optional": true,
             "description": "Websites' WebSQL data."
+          },
+          "cache": {
+            "type": "boolean",
+            "optional": true,
+            "description": "The Websites' cache data. Note: when removing data, this clears the <em>entire</em> cache: it is not limited to the range you specify."
           }
         }
       },
       {
         "id": "RemovalOptions",
         "type": "object",
         "description": "Options that determine exactly what data will be removed.",
         "properties": {
           "since": {
             "type": "number",
@@ skipping 433 matching lines @@
             "type": "function",
             "description": "Called when deletion has completed.",
             "optional": true,
             "parameters": []
           }
         ]
       }
     ]
   }
 ]