### New:  
(related #1019)
1. Adds bindings to GrBackendTextures::MakeGL 
2. Adds bindings to SkImages::AdoptTextureFrom
3. Adds bindings to GrBackendTextures::GLTextureParametersModdified

### Changes in build scripts:
(related #742)
1. Add file paths treating if building on Windows machine
2. Use "emcc.bat" instead of "emcc" if building on Windows machine, as
described on Emscripten website

### Use-case: 
Allows skia to draw images, rendered externally on gpu.
Compose would benefit greatly, allowing to embed VideoPlayer or Browser
without any friction or need to use Swing.