code: function mergeIntoMasterAndAddBundle(opts) {
  	var mains = opts.mains;
  	var loader = opts.loader;
  	var newGraph = opts.newGraph;
  	var bundleName = opts.bundleName;
  	var masterGraph = opts.masterGraph;
  
  	for(var name in newGraph) {
  		var oldNode = masterGraph[name];
  		var newNode = newGraph[name];
  
  		if(!oldNode || hasNewDeps(oldNode, newNode)) {
  			masterGraph[name] = newGraph[name];
  		}
  		// If it's a plugin we'll use the new node but need to copy any previous
  		// bundles onto the new node
  		else if(masterGraph[name] && masterGraph[name].isPlugin) {
  			var oldBundle = masterGraph[name].bundles || [];
  			masterGraph[name] = newGraph[name];
  			oldBundle.forEach(function(bundle){
  				addBundle(masterGraph[name], bundle);
  			});
  		}
  		// If this is the configMain like package.json!npm we need to override
  		// the source every time because it continuously changes.
  		else if(masterGraph[name] && name === loader.configMain) {
  			var node = masterGraph[name];
  			node.load.source = newGraph[name].load.source;
  		}
  
  		// do not track bundles of entry point modules (a.k.a mains) unless
  		// it is its own bundle.
  		if (name === bundleName || !includes(mains, name)) {
  			addBundle(masterGraph[name], bundleName);
  		}
  	}
  }
docs: merges everything in `newGraph` into `masterGraph` and make sure it lists `bundle` as one of its bundles.