Process message condensing in narrow.activate rather than hashchange.

Previously, we were having this problem where:
* You narrow to something
* That causes message_list.js:process_collapsing to run on all of the
  elements in the view, which changes some of their sizes
* That causes the pane to scroll and either push the content up or
  down, depending (since stuff on top of where you were is now a
  different size)
* That triggers keep_pointer_in_view, which moves your pointer

Moving process_collapsing into narrow.activate doesn't obviously
fix any of this, but it does seem to mitigate the issue a bit.

In particular, we (a) process it less frequently, and (b) process it
immediately after we show the narrowed view table, which seems to
reduce the raciness of the overall experience.

This does, however, introduce a regression:
* If you receive a long message when you're on
  #settings, e.g., and then go back to Home,
  the message does not properly get a [More] appended
  to it.

(imported from commit b1440d656cc7b71eca8af736f2f7b3aa7e0cca14)

zephyr/static/js/message_list.js

@@ -24,42 +24,6 @@ function MessageList(table_name, filter, opts) {
     return this;
 }
 
-function process_collapsing(index, elem) {
-    var content = $(elem).find(".message_content")[0];
-    var message = current_msg_list.get(rows.id($(elem)));
-    if (content !== undefined && message !== undefined) {
-        // If message.expanded is defined, then the user has manually
-        // specified whether this message should be expanded or collapsed.
-        if (message.expanded === true) {
-            $(content).addClass("expanded");
-            $(elem).find(".message_collapser").show();
-            $(elem).find(".message_expander").hide();
-            return;
-        } else if (message.expanded === false) {
-            $(content).removeClass("expanded");
-            $(elem).find(".message_expander").show();
-            $(elem).find(".message_collapser").hide();
-            return;
-        }
-
-        // We've limited the height of all elements in CSS.
-        // If offsetHeight < scrollHeight, then our CSS height limit has taken
-        // effect and we should show an expander button.
-        // If offsetHeight is only slightly smaller than scrollHeight, then we
-        // would only be collapsing by a small amount, which can be annoying.
-        // Instead of showing an expander button, just expand that element instead
-        // of keeping it collapsed.  (This also solves a bug seen on some Mac
-        // systems where offsetHeight == scrollHeight-1 for no apparent reason).
-        if (content.offsetHeight === 0 && content.scrollHeight === 0) {
-            return;
-        } else if (content.offsetHeight + 250 < content.scrollHeight) {
-            $(elem).find(".message_expander").show();
-        } else if (content.offsetHeight < content.scrollHeight) {
-            $(content).addClass("expanded");
-        }
-    }
-}
-
 (function () {
 
 function add_display_time(message, prev) {
@@ -433,7 +397,7 @@ MessageList.prototype = {
                               }});
         }
 
-        $.each(rendered_elems, process_collapsing);
+        $.each(rendered_elems, ui.process_collapsing);
 
         // Re-add the fading of messages that is lost when we re-render.
         compose.update_faded_messages();
@@ -566,8 +530,5 @@ $(document).on('message_selected.zephyr hashchange.zephyr mousewheel mousemove',
     // TODO: Figure out how to limit this animation stop to just the autoscroll
     $("html, body").stop();
 });
-$(document).on('hashchange.zephyr', function (event) {
-    $("tr.message_row").each(process_collapsing);
-});
 }());
 /*jslint nomen: false */

zephyr/static/js/narrow.js

@@ -413,6 +413,13 @@ exports.activate = function (operators, opts) {
     $("#zhome").removeClass("focused_table");
     $("#zfilt").css("opacity", 0).animate({opacity: 1});
 
+    // Deal with message condensing/uncondensing.
+    // In principle, this code causes us to scroll around because divs
+    // above us could change size -- which is problematic, because it
+    // could cause us to lose our position. But doing this here, right
+    // after showing the table, seems to cause us to win the race.
+    $("tr.message_row").each(ui.process_collapsing);
+
     reset_load_more_status();
     if (! defer_selecting_closest) {
         maybe_select_closest();

zephyr/static/js/ui.js

@@ -1345,6 +1345,42 @@ exports.restore_compose_cursor = function () {
         .caret(saved_compose_cursor, saved_compose_cursor);
 };
 
+exports.process_collapsing = function (index, elem) {
+    var content = $(elem).find(".message_content")[0];
+    var message = current_msg_list.get(rows.id($(elem)));
+    if (content !== undefined && message !== undefined) {
+        // If message.expanded is defined, then the user has manually
+        // specified whether this message should be expanded or collapsed.
+        if (message.expanded === true) {
+            $(content).addClass("expanded");
+            $(elem).find(".message_collapser").show();
+            $(elem).find(".message_expander").hide();
+            return;
+        } else if (message.expanded === false) {
+            $(content).removeClass("expanded");
+            $(elem).find(".message_expander").show();
+            $(elem).find(".message_collapser").hide();
+            return;
+        }
+
+        // We've limited the height of all elements in CSS.
+        // If offsetHeight < scrollHeight, then our CSS height limit has taken
+        // effect and we should show an expander button.
+        // If offsetHeight is only slightly smaller than scrollHeight, then we
+        // would only be collapsing by a small amount, which can be annoying.
+        // Instead of showing an expander button, just expand that element instead
+        // of keeping it collapsed.  (This also solves a bug seen on some Mac
+        // systems where offsetHeight == scrollHeight-1 for no apparent reason).
+        if (content.offsetHeight === 0 && content.scrollHeight === 0) {
+            return;
+        } else if (content.offsetHeight + 250 < content.scrollHeight) {
+            $(elem).find(".message_expander").show();
+        } else if (content.offsetHeight < content.scrollHeight) {
+            $(content).addClass("expanded");
+        }
+    }
+};
+
 exports.update_recent_subjects = function () {
     function same(arr1, arr2) {
         var i = 0;