Add a context field to the accessibility extension API.

chrome/common/extensions/api/extension_api.json

 [
   {
     "namespace": "experimental.accessibility",
     "nodoc": true,
     "types": [
       {
         "id": "AccessibilityObject",
         "type": "object",
         "description": "Parent class for accessibility information about an object.",
         "properties": {
           "type": {
             "type": "string",
             "description": "The type of this object, which determines the contents of 'details'.",
             "enum": ["button", "checkbox", "combobox", "link", "menu", "menuitem", "radiobutton", "tab", "textbox", "window"]
           },
           "name": {
             "type": "string",
             "description": "The localized name of the object, like OK or Password. Do not rely on an exact string match because the text will be in the user's language and may change in the future."
           },
+          "context": {
+            "type": "string",
+            "description": "The localized name of the context for the object, like the name of the surrounding toolbar or group of controls.",
+            "optional": true
+          },
           "details": {
             "description": "Other details like the state, depending on the type of object.",
             "optional": true,
             "choices": [
               { "$ref": "CheckboxDetails" },
               { "$ref": "ComboBoxDetails" },
               { "$ref": "MenuDetails" },
               { "$ref": "MenuItemDetails" },
               { "$ref": "RadioButtonDetails" },
               { "$ref": "TabDetails" },
@@ skipping 9210 matching lines @@
                 "enum": ["enabled", "disabled", "forced"],
                 "description": "Exposes whether the incognito mode is available to windows. One of 'enabled', 'disabled' (user cannot browse pages in Incognito mode), 'forced' (all pages/sessions are forced into Incognito mode)."
               }
             ]
           }
         ]
       }
     ]
   }
 ]