Summary:
This adds support for specifying multiple sources for an image component, so that native can choose the best one based on the flexbox-computed size of the image.
The API is as follows: the image component receives in the `source` prop an array of objects of the type `{uri, width, height}`. On the native side, the native component will wait for the layout pass to receive the width and height of the image, and then parse the array to find the best fitting one. For now, this does not support local resources, but it will be added soon.
To see how this works and play with it, there's an example called `MultipleSourcesExample` under `ImageExample` In UIExplorer.
Reviewed By: foghina
Differential Revision: D3364550
fbshipit-source-id: 66c5aeb2794f2ffeff8da39a9c0b95155fb2d41f
617a38d984