function registerBackend(name, factory, priority) {
	  if (priority === void 0) {
	    priority = 1;
	  }

	  return ENGINE.registerBackend(name, factory, priority);
	}
Registers a global backend. The registration should happen when importing
a module file (e.g. when importing `backend_webgl.ts`), and is used for
modular builds (e.g. custom tfjs bundle with only webgl support).

@param factory The backend factory function. When called, it should
return a backend instance, or a promise of an instance.
@param priority The priority of the backend (higher = more important).
    In case multiple backends are registered, the priority is used to find
    the best backend. Defaults to 1.
@return False if there is already a registered backend under this name, true
    if not.

@doc {heading: 'Backends'}