Add SwiftShader source to repo
Oct 6 code drop from Transgaming
Review URL: https://chromereviews.googleplex.com/
3846015
Add header for swiftshader.
This header will be included in builds that use swiftshader, and will be used to avoid having a watermark on images.
Review URL: https://chromereviews.googleplex.com/
3765016
Add Readme.txt with legal info.