Add scroll event handling to webagg backend

Conflicts:
	lib/matplotlib/backends/backend_webagg_core.py

Conflicts:
	lib/matplotlib/backends/backend_webagg_core.py
	lib/matplotlib/backends/web_backend/mpl.js

Author: blink1073

lib/matplotlib/backends/web_backend/mpl.js

@@ -143,6 +143,7 @@ mpl.figure.prototype._init_canvas = function() {
     // Throttle sequential mouse events to 1 every 20ms.
     rubberband.mousemove('motion_notify', mouse_event_fn);
 
+<<<<<<< HEAD
     rubberband.mouseenter('figure_enter', mouse_event_fn);
     rubberband.mouseleave('figure_leave', mouse_event_fn);
 
@@ -152,6 +153,31 @@ mpl.figure.prototype._init_canvas = function() {
         event.step = event.deltaY / 3.
         mouse_event_fn(event);
     });
+=======
+
+    rubberband.mouseenter('figure_enter', mouse_event_fn);
+    rubberband.mouseleave('figure_leave', mouse_event_fn);
+
+    function scroll_fn(event) {
+        event['data'] = 'scroll'
+        // http://www.adomas.org/javascript-mouse-wheel/
+        if (event.wheelDelta) { /* IE/Opera. */
+                event.step = event.wheelDelta/120;
+        } else if (event.detail) { /** Mozilla case. */
+            /** In Mozilla, sign of delta is different than in IE.
+             * Also, delta is multiple of 3.
+             */
+            event.step = -event.detail/3;
+        }
+        mouse_event_fn(event)
+    }
+    // Initialization code. 
+    if (window.addEventListener)
+        /** DOMMouseScroll is for mozilla. */
+        window.addEventListener('DOMMouseScroll', scroll_fn, false);
+    /** IE/Opera. */
+    window.onmousewheel = document.onmousewheel = scroll_fn;
+>>>>>>> fe99b32... Add scroll event handling to webagg backend
 
     canvas_div.append(canvas);
     canvas_div.append(rubberband);