Subframes in inner WebContents should not create proxies in process of outer WebContents.

chrome/test/data/extensions/platform_apps/web_view/shim/manifest.json

 {
   "name": "Platform App Test: <webview>",
   "version": "2",
   "permissions": [
     "webview"
   ],
   "app": {
     "background": {
       "scripts": ["test.js"]
     }
   },
   "webview": {
     "partitions": [
       {
         "name": "foobar",
         "accessible_resources": [
+          "child_frame.html",
+          "parent_frame.html",
           "guest_with_inline_script.html",
           "test.pdf"
         ]
       }
     ]
   }
 }