Merge pull request matplotlib#3969 from blink1073/add-resize-event-webagg

BUG : Connect the Resize Event for WebAgg

Author: tacaswell

lib/matplotlib/backends/backend_webagg_core.py

@@ -252,6 +252,7 @@ def handle_resize(self, event):
         # identical or within a pixel or so).
         self._png_is_old = True
         self.manager.resize(w, h)
+        self.resize_event()
 
     def handle_send_image_mode(self, event):
         # The client requests notification of what the current image mode is.