Summary:
@vjeux and I were discussing this in irc an discovered that network gif images did not respond how they should to width, height or flex properties. Along the way I also noticed that the scale was not changing depending on the device. This PR fixes that, so now you can do `flex: 1` on a gif image to have it stretch to the whole screen. [Minimum reproducible example here](https://gist.github.com/brentvatne/f745377b0789162a28df) - try this without and then with the changes of this PR to see.
Closes https://github.com/facebook/react-native/pull/353
Github Author: Brent Vatne <brent.vatne@madriska.com>
Test Plan: Imported from GitHub, without a `Test Plan:` line.
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