Update chrome zoomed offset patch to use body

Rather than using an element absolutely positioned at 0,0, compute
compensation value based on offset of body. This should be tested more
rigorously but on the upside it does avoid further manipulating the DOM.

src/core.js

@@ -35,8 +35,7 @@ var DATA_DISPLAYCONTROLLER = 'displayController',
 		'mouseenter',
 		'mouseleave',
 		'contextmenu'
-	],
-	PATCH_DUMMY_ELEMENT_ID = 'chromeBugOffsetRef';
+	];
 
 /**
  * Session data
@@ -99,7 +98,7 @@ $.fn.powerTip = function(opts, arg) {
 		return $.powerTip[opts].call(targetElements, targetElements, arg);
 	}
 
-	injectChromePatchReferenceElement();
+	activateChromeZoomedOffsetPatch();
 
 	// extend options
 	options = $.extend({}, $.fn.powerTip.defaults, opts);

src/utility.js

@@ -203,13 +203,17 @@ function countFlags(value) {
 }
 
 /**
- * Conditionally insert reference element for use in Chrome zoomed offset patch
+ * Conditionally make reference for Chrome zoomed offset patch
+ *
  * Reference https://bugs.chromium.org/p/chromium/issues/detail?id=489206
+ * Suggested patch calls for inserting an absolutely positioned element at 0,0.
+ * However, it appears that document.body serves equally well as a references
+ * and avoid needing to manipulate DOM. Beware offset behavior when body is not
+ * positioned at 0,0.
  */
-function injectChromePatchReferenceElement() {
-	if (/Chrome\/[.0-9]*/.test(navigator.userAgent) && !document.getElementById(PATCH_DUMMY_ELEMENT_ID)) {
-		session.chromePatchRefElement = $('<div id="' + PATCH_DUMMY_ELEMENT_ID +
-			'" style="position: absolute; left: 0px; top: 0px; width: 1px; height: 1px; visibility: hidden"></div>').prependTo(document.body);
+function activateChromeZoomedOffsetPatch() {
+	if (/Chrome\/[.0-9]*/.test(navigator.userAgent)) {
+		session.chromePatchRefElement = $(document.body);
 	}
 }
 
@@ -222,10 +226,10 @@ function injectChromePatchReferenceElement() {
 function getCompensatedOffset(element) {
 	if (session.chromePatchRefElement) {
 		var offset = element.offset();
-		var rd = session.chromePatchRefElement[0].getBoundingClientRect();
+		var r = session.chromePatchRefElement.offset();
 		return {
-			left: offset.left - (rd.left + window.pageXOffset),
-			top: offset.top - (rd.top + window.pageYOffset)
+			left: offset.left - r.left,
+			top: offset.top - r.top
 		};
 	}
 	return element.offset();