[ios] Fixes layout of the sync encryption passphrase screen.

We were changing to a bold weight font in
collectionView:cellForRowAtIndexPath:.  This was causing the text to
reflow onto three lines instead of two, but the collection view didn't
know that it needed to recompute cell heights, causing a rendering
issue.  This CL works around the issue by leaving the font at a normal
weight, so that no text reflow occurs.

BUG=864495

Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I3ec847752dbddad8460d27f4d051952bc46fa54f
Reviewed-on: https://chromium-review.googlesource.com/1147144Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577895}

ios/chrome/browser/ui/settings/sync_encryption_passphrase_collection_view_controller.mm

@@ -326,12 +326,13 @@ const CGFloat kSpinnerButtonPadding = 18;
   CollectionViewItem* item =
       [self.collectionViewModel itemAtIndexPath:indexPath];
   if (item.type == ItemTypeMessage) {
-    CardMultilineCell* messageCell =
-        base::mac::ObjCCastStrict<CardMultilineCell>(cell);
-    if (experimental_flags::IsSettingsUIRebootEnabled()) {
-      messageCell.textLabel.font =
-          [UIFont boldSystemFontOfSize:kUIKitMainFontSize];
-    } else {
+    // Changing the font weight may reflow the text onto a different number of
+    // lines, but the collection view doesn't know that it needs to layout the
+    // cell again. Sidestep this bug by leaving the font at a normal weight
+    // under UIRefresh.
+    if (!experimental_flags::IsSettingsUIRebootEnabled()) {
+      CardMultilineCell* messageCell =
+          base::mac::ObjCCastStrict<CardMultilineCell>(cell);
       messageCell.textLabel.font =
           [[MDCTypography fontLoader] mediumFontOfSize:14];
     }