Add cleanup for resize listeners on message editing.

I changed the watch_manual_resize function to return the listener
functions it creates, and then these are used to remove the event
listeners before the edit box is hidden.

static/js/message_edit.js

@@ -220,7 +220,8 @@ function edit_message(row, raw_content) {
         initClipboard(copy_message[0]);
     } else if (editability === editability_types.FULL) {
         copy_message.remove();
-        resize.watch_manual_resize("#message_edit_content");
+        var listeners = resize.watch_manual_resize("#message_edit_content");
+        currently_editing_messages[rows.id(row)].listeners = listeners;
         composebox_typeahead.initialize_compose_typeahead("#message_edit_content", {emoji: true, stream: true});
     }
 
@@ -360,6 +361,13 @@ exports.end = function (row) {
         currently_editing_messages[message.id] !== undefined) {
         var scroll_by = currently_editing_messages[message.id].scrolled_by;
         message_viewport.scrollTop(message_viewport.scrollTop() - scroll_by);
+
+        // Clean up resize event listeners
+        var listeners = currently_editing_messages[message.id].listeners;
+        var edit_box = document.querySelector("#message_edit_content");
+        edit_box.removeEventListener("mousedown", listeners[0]);
+        document.body.removeEventListener("mouseup", listeners[1]);
+
         delete currently_editing_messages[message.id];
         current_msg_list.hide_edit_message(row);
     }

static/js/resize.js

@@ -166,21 +166,22 @@ function left_userlist_get_new_heights() {
 }
 
 exports.watch_manual_resize = function (element) {
-    (function on_box_resize(cb) {
+    return (function on_box_resize(cb) {
         var meta = {
             box: document.querySelector(element),
             height: null,
             mousedown: false,
         };
 
-        meta.box.addEventListener("mousedown", function () {
+        var box_handler = function () {
             meta.mousedown = true;
             meta.height = meta.box.clientHeight;
-        });
+        };
+        meta.box.addEventListener("mousedown", box_handler);
 
         // If the user resizes the textarea manually, we use the
         // callback to stop autosize from adjusting the height.
-        document.body.addEventListener("mouseup", function () {
+        var body_handler = function () {
             if (meta.mousedown === true) {
                 meta.mousedown = false;
                 if (meta.height !== meta.box.clientHeight) {
@@ -188,7 +189,10 @@ exports.watch_manual_resize = function (element) {
                     cb.call(meta.box, meta.height);
                 }
             }
-        });
+        };
+        document.body.addEventListener("mouseup", body_handler);
+
+        return [box_handler, body_handler];
     }(function (height) {
         // This callback disables autosize on the textarea.  It
         // will be re-enabled when this component is next opened.

static/styles/zulip.css

@@ -1294,6 +1294,7 @@ div.focused_table {
 .message_edit_content {
     line-height: 18px;
     resize: vertical!important;
+    max-height: 24em;
 }
 
 .message_edit_countdown_timer {