[Media Router] Return NotFoundError on dialog exit if appropriate

chrome/test/media_router/resources/README.md

 The document shows how to create a test data file which is used for the
 integration test to inject test data before running test.
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 The test data is a JSON string and here is full example with description:
 
 {
   // Define the return value for getAvailableSinks API defined in
   // TestProvider.js.
-  // The return value is a list as following. Default value is:
+  // The value is a map from source urn to a list of sinks as following. Default
+  // value is for test source urn only and is:
   // [{"id": "id1", "friendlyName": "test-sink-1"},
   //  {"id": "id2", "friendlyName": "test-sink-2"}]
-  "getAvailableSinks": [{"id": "id1", "friendlyName": "test-device-1"},
-                        {"id": "id2", "friendlyName": "test-device-2"}],
+  "getAvailableSinks": {
+    "http://www.google.com/": [
+      {"id": "id1", "friendlyName": "test-device-1"},
+      {"id": "id2", "friendlyName": "test-device-2"}
+    ]
+  },
 
   // Define the return value for canRoute API, the return value should be
   // either 'true' or 'false'. The default value is 'true'.
   "canRoute": "true",
 
   // Define the return value for createRoute API. Since the return type of
   // createRoute is a Promise, here we just need to define
   // if return successful result or error.
   // The value for 'passed' should be either 'true' or 'false'.
   // If it is 'false', you also need to give the corresponding
   // error message. If it is 'true', the error message will be ignored.
   // TODO(leilei): Change keyword 'passed' to 'success'.
   "createRoute": {"passed": "false", "errorMessage": "Unknown sink"}
 }