Patch for powertip offset bug when zoomed on Blink render

Reference getBoundingClientRect behavior in
https://bugs.chromium.org/p/chromium/issues/detail?id=489206

src/core.js

@@ -35,7 +35,8 @@ var DATA_DISPLAYCONTROLLER = 'displayController',
 		'mouseenter',
 		'mouseleave',
 		'contextmenu'
-	];
+	],
+	PATCH_DUMMY_ELEMENT_ID = 'chromeBugOffsetRef';
 
 /**
  * Session data
@@ -60,7 +61,8 @@ var session = {
 	windowWidth: 0,
 	windowHeight: 0,
 	scrollTop: 0,
-	scrollLeft: 0
+	scrollLeft: 0,
+	chromePatchRefElement: null
 };
 
 /**
@@ -97,6 +99,8 @@ $.fn.powerTip = function(opts, arg) {
 		return $.powerTip[opts].call(targetElements, targetElements, arg);
 	}
 
+	injectChromePatchReferenceElement();
+
 	// extend options
 	options = $.extend({}, $.fn.powerTip.defaults, opts);
 

src/placementcalculator.js

@@ -99,7 +99,7 @@ function PlacementCalculator() {
 	 * @return {Object} An object with the top,left position values.
 	 */
 	function getHtmlPlacement(element, placement) {
-		var objectOffset = element.offset(),
+		var objectOffset = getCompensatedOffset(element),
 			objectWidth = element.outerWidth(),
 			objectHeight = element.outerHeight(),
 			left,

src/utility.js

@@ -109,7 +109,7 @@ function isMouseOver(element) {
 	// methods do not work with SVG elements
 	// compute width/height because those properties do not exist on the object
 	// returned by getBoundingClientRect() in older versions of IE
-	var elementPosition = element.offset(),
+	var elementPosition = getCompensatedOffset(element),
 		elementBox = element[0].getBoundingClientRect(),
 		elementWidth = elementBox.right - elementBox.left,
 		elementHeight = elementBox.bottom - elementBox.top;
@@ -201,3 +201,32 @@ function countFlags(value) {
 	}
 	return count;
 }
+
+/**
+ * Conditionally insert reference element for use in Chrome zoomed offset patch
+ * Reference https://bugs.chromium.org/p/chromium/issues/detail?id=489206
+ */
+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);
+	}
+}
+
+/**
+ * Compensate for the Chrome getBoundingClientRect bug when zoomed.
+ * Reference https://bugs.chromium.org/p/chromium/issues/detail?id=489206
+ * @param {jQuery} element The element that the tooltip should target.
+ * @return {Offsets} The top, left offsets relative to the document.
+ */
+function getCompensatedOffset(element) {
+	if (session.chromePatchRefElement) {
+		var offset = element.offset();
+		var rd = session.chromePatchRefElement[0].getBoundingClientRect();
+		return {
+			left: offset.left - (rd.left + window.pageXOffset),
+			top: offset.top - (rd.top + window.pageYOffset)
+		};
+	}
+	return element.offset();
+}