Enable Polymer.Settings.useNativeShadow on the dashboard.

third_party/flot/jquery.flot.js

 /* Javascript plotting library for jQuery, version 0.8.3.
 
 Copyright (c) 2007-2014 IOLA and Ole Laursen.
 Licensed under the MIT license.
 
 */
 
 // first an inline dependency, jquery.colorhelpers.js, we inline it here
 // for convenience
 
@@ skipping 627 matching lines @@
         // public functions
         plot.setData = setData;
         plot.setupGrid = setupGrid;
         plot.draw = draw;
         plot.getPlaceholder = function() { return placeholder; };
         plot.getCanvas = function() { return surface.element; };
         plot.getPlotOffset = function() { return plotOffset; };
         plot.width = function () { return plotWidth; };
         plot.height = function () { return plotHeight; };
         plot.offset = function () {
-            var o = eventHolder.offset();
+            var o = eventHolder[0].getBoundingClientRect();
             o.left += plotOffset.left;
             o.top += plotOffset.top;
             return o;
         };
         plot.getData = function () { return series; };
         plot.getAxes = function () {
             var res = {}, i;
             $.each(xaxes.concat(yaxes), function (_, axis) {
                 if (axis)
                     res[axis.direction + (axis.n != 1 ? axis.n : "") + "axis"] = axis;
@@ skipping 2280 matching lines @@
         }
 
         function onClick(e) {
             triggerClickHoverEvent("plotclick", e,
                                    function (s) { return s["clickable"] != false; });
         }
 
         // trigger click or hover event (they send the same parameters
         // so we share their code)
         function triggerClickHoverEvent(eventname, event, seriesFilter) {
-            var offset = eventHolder.offset(),
-                canvasX = event.pageX - offset.left - plotOffset.left,
-                canvasY = event.pageY - offset.top - plotOffset.top,
+            // When Polymer.useNativeShadow is false, eventHolder.offset() works
+            // because $.contains(document.documentElement, eventHolder[0]) is
+            // true. When Polymer.useNativeShadow is true, $.contains() is false
+            // when there is a shadow root between document.documentElement and
+            // eventHolder[0].
+            var offset = eventHolder[0].getBoundingClientRect();
+            var canvasX = event.pageX - offset.left - plotOffset.left;
+            var canvasY = event.pageY - offset.top - plotOffset.top;
             pos = canvasToAxisCoords({ left: canvasX, top: canvasY });
 
             pos.pageX = event.pageX;
             pos.pageY = event.pageY;
 
             var item = findNearbyItem(canvasX, canvasY, seriesFilter);
 
             if (item) {
                 // fill in mouse pos for any listeners out there
                 item.pageX = parseInt(item.series.xaxis.p2c(item.datapoint[0]) + offset.left + plotOffset.left, 10);
@@ skipping 197 matching lines @@
             $.plot(this, data, options);
         });
     };
 
     // round to nearby lower multiple of base
     function floorInBase(n, base) {
         return base * Math.floor(n / base);
     }
 
 })(jQuery);