Adds parsing for the app_id field from an "open-with-" link

chrome/test/data/chromeos/gdata/basic_feed.json

 {
    "encoding": "UTF-8",
    "feed": {
       "author": [ {
          "email": {
             "$t": "tester@testing.com"
          },
          "name": {
             "$t": "tester"
          }
@@ skipping 66 matching lines @@
             "rel": "http://schemas.google.com/g/2005#resumable-create-media",
             "type": "application/atom+xml"
          }, {
             "href": "https://1_self_link",
             "rel": "self",
             "type": "application/atom+xml"
          }, {
             "href": "https://1_edit_link",
             "rel": "edit",
             "type": "application/atom+xml"
-         } ],
+         }  ],
          "published": {
             "$t": "2010-11-07T05:03:54.719Z"
          },
          "title": {
             "$t": "Entry 1 Title"
          },
          "updated": {
             "$t": "2011-04-01T18:34:08.234Z"
          }
       }, {
@@ skipping 73 matching lines @@
             "rel": "self",
             "type": "application/atom+xml"
          }, {
             "href": "https://file_link_edit",
             "rel": "edit",
             "type": "application/atom+xml"
          }, {
             "href": "https://file_edit_media",
             "rel": "edit-media",
             "type": "audio/mpeg"
+         },  {
+            "href": "https://xml_file_entry_open_with_link/",
+            "rel": "http://schemas.google.com/docs/2007#open-with-the_app_id",
+            "type": "application/atom+xml"
+         },  {
+            "href": "https://xml_file_fake_entry_open_with_link/",
+            "rel": "http://schemas.google.com/docs/2007#oh-no-not-open-with-the_app_id",
+            "type": "application/atom+xml"
          } ],
          "published": {
             "$t": "2011-12-14T00:40:47.330Z"
          },
          "title": {
             "$t": "winter.m4a"
          },
          "updated": {
             "$t": "2011-12-14T00:40:47.330Z"
          }
@@ skipping 205 matching lines @@
       },
       "xmlns": "http://www.w3.org/2005/Atom",
       "xmlns$batch": "http://schemas.google.com/gdata/batch",
       "xmlns$docs": "http://schemas.google.com/docs/2007",
       "xmlns$gd": "http://schemas.google.com/g/2005",
       "xmlns$openSearch": "http://a9.com/-/spec/opensearch/1.1/"
    },
    "version": "1.0"
 }