右クリック＋ホイールでズームレベル変更（たしかChromeのみ動く）

zoom.js

!function(){
	var zoom_active = false
	var zoom_change = false
	var zoom_per = 1.08
	
	var init = function(){
		document.body.style.zoom = 1
	}
	if(document.readyState === "complete"){
		init()
	}else{
		window.addEventListener("load", init, false)
	}
	
	window.addEventListener("mousedown", function(eve){
		eve.button === 2 && (zoom_active = true, zoom_change = false)
		eve.button === 1 && zoom_active && init()
	}, true)
	
	window.addEventListener("mouseup", function(eve){
		eve.button === 2 && (zoom_active = false)
	}, true)
	
	window.addEventListener("mousewheel", function(eve){
		if(zoom_active){
			if(eve.deltaY < 0){ // zoom in
				window.top.document.body.style.zoom *= zoom_per
			}else if(eve.deltaY > 0){ // zoom out
				window.top.document.body.style.zoom /= zoom_per
			}
			zoom_change = true
			eve.preventDefault()
		}
	}, true)
	
	// cancel right click action when zoom was changed
	window.addEventListener("contextmenu", function(eve){
		zoom_change && eve.preventDefault()
	}, false)
}()