simple mapping of native methods to javascript implementations.

[johanvos]

This fixes #42
As an example, native methods in JavaFX rendering code
For example:

private static native void nTexSubImage2D0(int target, int level,
            int xoffset, int yoffset, int width, int height, int format,
            int type, Object pixels, int pixelsByteOffset);

(see https://github.com/openjdk/jfx/blob/master/modules/javafx.graphics/src/main/java/com/sun/prism/es2/GLContext.java#L185)

maps to

function native_com_sun_prism_es2_GLContext_nTexSubImage2D0(target, level,
        xoffset, yoffset, width, height, format, type, pixels, pixelsByteOffset) {

(see https://github.com/gluonhq/uongl/blob/master/src/main/javascript/uongl.js#L451)

This allows existing libraries with JNI to be used without having access to the code.

[jtulach]

Where does the native_com_sun_prism_es2_GLContext_nTexSubImage2D0 method come from? From a global scope? That's nasty. Bck2Brwsr tries to limit the number of globally visible symbols - only bck2brwsr symbol is available after booting. The rest is hidden in each Bck2Brwsr generated .js file.

Exposing new contract via global scope seems a bit too hacky. I'd rather recommend to use (more verbose, but) existing contract as shown in fe5bdfa. It should cover the same cases (except when the native method is called in static class initializer).