Use -traitCollectionDidChange: to detect size class changes

This is simpler than -viewWillTransitionToSize:withTransitionCoordinator:
because all the logic is in one place, ContentSuggestionsHeaderView.

Bug: 965964
Change-Id: Id990d4b91e07282f7ff985f529c5ad27856f0199
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1626302Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Peter Lee <pkl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662621}

ios/chrome/browser/ui/content_suggestions/content_suggestions_header_view.h

@@ -41,13 +41,6 @@
 // Can only be added once.
 - (void)addToolbarView:(UIView*)toolbarView;
 
-// Adjusts the autolayout constraints for |identityDiscView| when
-// UIViewController changes size. When an iPhone is rotated from portrait
-// (no top toolbar) to landscape (with top toolbar), the placement of Identity
-// Disc has to be shifted down below the top toolbar. Otherwise, the Identity
-// Disc may be obscured by the top toolbar in landscape mode.
-- (void)adjustIdentityDiscConstraints;
-
 // Returns the progress of the search field position along
 // |ntp_header::kAnimationDistance| as the offset changes.
 - (CGFloat)searchFieldProgressForOffset:(CGFloat)offset

ios/chrome/browser/ui/content_suggestions/content_suggestions_header_view.mm

@@ -54,8 +54,8 @@ CGFloat ToolbarHeight() {
 
 // Returns the amount of vertical space to allow for the existence of a top
 // toolbar when iPhone is in landscape orientation.
-CGFloat IdentityDiscToolbarOffset() {
-  return IsCompactHeight() ? ToolbarHeight() : 0;
+CGFloat IdentityDiscToolbarOffset(id<UITraitEnvironment> environment) {
+  return IsCompactHeight(environment) ? ToolbarHeight() : 0;
 }
 
 }  // namespace
@@ -114,7 +114,7 @@ CGFloat IdentityDiscToolbarOffset() {
   id<LayoutGuideProvider> layoutGuide = self.safeAreaLayoutGuide;
   self.identityDiscTopConstraint = [self.identityDiscView.topAnchor
       constraintEqualToAnchor:layoutGuide.topAnchor
-                     constant:IdentityDiscToolbarOffset()];
+                     constant:IdentityDiscToolbarOffset(self)];
   CGFloat dimension =
       ntp_home::kIdentityAvatarDimension + 2 * ntp_home::kIdentityAvatarMargin;
   [NSLayoutConstraint activateConstraints:@[
@@ -126,15 +126,6 @@ CGFloat IdentityDiscToolbarOffset() {
   ]];
 }
 
-- (void)adjustIdentityDiscConstraints {
-  // identityDiscView may not be set.
-  if (!self.identityDiscView)
-    return;
-
-  DCHECK(IsIdentityDiscFeatureEnabled());
-  self.identityDiscTopConstraint.constant = IdentityDiscToolbarOffset();
-}
-
 - (void)addViewsToSearchField:(UIView*)searchField {
   // Fake Toolbar.
   ToolbarButtonFactory* buttonFactory =
@@ -405,6 +396,27 @@ CGFloat IdentityDiscToolbarOffset() {
                    completion:nil];
 }
 
+#pragma mark - UITraitEnvironment
+
+// Adjusts the autolayout constraints for |identityDiscView| when view changes
+// size. When an iPhone is rotated from portrait (no top toolbar) to landscape
+// (with top toolbar), the placement of Identity Disc has to be shifted down
+// below the top toolbar. Otherwise, the Identity Disc may be obscured by the
+// top toolbar in landscape mode.
+- (void)traitCollectionDidChange:(UITraitCollection*)previousTraitCollection {
+  [super traitCollectionDidChange:previousTraitCollection];
+  // identityDiscView may not be set if feature is not enabled.
+  if (!self.identityDiscView)
+    return;
+  DCHECK(IsIdentityDiscFeatureEnabled());
+  if ((self.traitCollection.verticalSizeClass !=
+       previousTraitCollection.verticalSizeClass) ||
+      (self.traitCollection.horizontalSizeClass !=
+       previousTraitCollection.horizontalSizeClass)) {
+    self.identityDiscTopConstraint.constant = IdentityDiscToolbarOffset(self);
+  }
+}
+
 #pragma mark - Property accessors
 
 - (UIView*)fakeLocationBar {

ios/chrome/browser/ui/content_suggestions/content_suggestions_header_view_controller.mm

@@ -265,20 +265,6 @@ using base::UserMetricsAction;
   return self.headerView;
 }
 
-#pragma mark - UIViewController
-
-- (void)viewWillTransitionToSize:(CGSize)size
-       withTransitionCoordinator:
-           (id<UIViewControllerTransitionCoordinator>)coordinator {
-  [super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
-  [coordinator
-      animateAlongsideTransition:^(
-          id<UIViewControllerTransitionCoordinatorContext> context) {
-        [self.headerView adjustIdentityDiscConstraints];
-      }
-                      completion:nil];
-}
-
 #pragma mark - Private
 
 // Initialize and add a search field tap target and a voice search button.