Correction of return parameter validation for popup.getParentWindow, and extension.getPopupView.

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 192 matching lines @@
     ]
   },
   {
     "namespace": "experimental.extension",
     "nodoc": true,
     "types": [],
     "functions": [
       {
         "name": "getPopupView",
         "type": "function",
-        "description": "Returns a reference to the window object of the popup view.",
+        "description": "Returns a reference to the window object of the popup view.  Returns undefined if no popup presently shown.",
         "parameters": [],
         "returns": {
           "type": "object",
           "isInstanceOf": "DOMWindow",
           "properties": {},
-          "additionalProperties": { "type": "any" }
+          "additionalProperties": { "type": "any" },
+          "optional": true
         }
       }
     ],
     "events": []
   },
   {
     "namespace": "windows",
     "types": [
       {
         "id": "Window",
@@ skipping 1441 matching lines @@
           {
             "type": "function",
             "name": "callback",
             "parameters": []
           }
         ]
       },
       {
         "name": "getParentWindow",
         "type": "function",
-        "description": "Returns a reference to the window object of the extension view that launched the popup.",
+        "description": "Returns a reference to the window object of the extension view that launched the popup.  Returns undefined if called outside of a popup window.",
         "parameters": [],
         "returns": {
           "type": "object",
           "isInstanceOf": "DOMWindow",
           "properties": {},
-          "additionalProperties": { "type": "any" }
+          "additionalProperties": { "type": "any" },
+          "optional": true
         }
       }
     ],
     "events": [
       {
         "name": "onClosed",
         "type": "function",
         "description": "Fired when the popup view is closed.",
         "parameters": []
       }
@@ skipping 48 matching lines @@
         "type": "function",
         "description": "Logs a message during internal unit testing.",
         "parameters": [
           {"type": "string", "name": "message"}
         ]
       }
     ],
     "events": []
   }
 ]