drive: Supports shared-with-me search in searchDriveMetadata().

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

 {
    "encoding": "UTF-8",
    "feed": {
       "author": [ {
          "email": {
             "$t": "tester@testing.com"
          },
          "name": {
             "$t": "tester"
          }
@@ skipping 277 matching lines @@
                "$t": "someoneelse@testing.com"
             },
             "name": {
                "$t": "someoneelse"
             }
          } ],
          "category": [ {
             "label": "audio/mpeg",
             "scheme": "http://schemas.google.com/g/2005#kind",
             "term": "http://schemas.google.com/docs/2007#file"
+         }, {
+            "label": "shared",
+            "scheme": "http://schemas.google.com/g/2005/labels",
+            "term": "http://schemas.google.com/g/2005/labels#shared"
+         }, {
+            "label": "shared-with-me",
+            "scheme": "http://schemas.google.com/g/2005/labels",
+            "term": "http://schemas.google.com/g/2005/labels#shared-with-me"
          } ],
          "content": {
             "src": "https://file_content_url/",
             "type": "audio/mpeg"
          },
          "docs$filename": {
             "$t": "Shared To The Account Owner.txt"
          },
          "docs$md5Checksum": {
             "$t": "3b4382ebefec6e743578c76bbd0575ce"
@@ skipping 1021 matching lines @@
          "$t": "2011-12-14T01:03:21.151Z"
       },
       "xmlns": "http://www.w3.org/2005/Atom",
       "xmlns$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"
 }