The code asked all media sources for a rerender and used whichever one
came in first, which meant that it might potentially render the wrong
image, or reject the promise if one source served an error response
before a good response from another source arrived.
Also reject the promise if we can't find an image source in the response.
Change-Id: I6b516ad41b8a9e2abd440625bb76f3e1abb54520
Using the MW APIs get a resized version of the image and use
GeneratedContentNode to cache the url.
Bug: 55697
Change-Id: I418f7e1464663f447d46de7ffc29aa5f52d23b12