Update fake omnibox width on rotation

When rotating the device, the omnibox width should be set to the new
width. This width computation needs to take into account the y offset
of the collection and its new size.
So the calculation needs to be started from the collection.

Bug: 750637
Change-Id: I14dc8f878b815f7f32bd33f88691e9b39782e0d4
Reviewed-on: https://chromium-review.googlesource.com/595741Reviewed-by: Elodie Banel <lod@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490956}

ios/chrome/browser/content_suggestions/content_suggestions_header_view_controller.mm

@@ -124,21 +124,6 @@ const CGFloat kHintLabelSidePadding = 12;
     [self.headerView hideToolbarViewsForNewTabPage];
 }
 
-#pragma mark - UIViewController
-
-- (void)viewWillTransitionToSize:(CGSize)size
-       withTransitionCoordinator:
-           (id<UIViewControllerTransitionCoordinator>)coordinator {
-  [super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
-
-  void (^alongsideBlock)(id<UIViewControllerTransitionCoordinatorContext>) =
-      ^(id<UIViewControllerTransitionCoordinatorContext> context) {
-        [self.fakeOmniboxWidthConstraint
-            setConstant:content_suggestions::searchFieldWidth(size.width)];
-      };
-  [coordinator animateAlongsideTransition:alongsideBlock completion:nil];
-}
-
 #pragma mark - ContentSuggestionsHeaderControlling
 
 - (void)updateSearchFieldForOffset:(CGFloat)offset {

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

@@ -210,6 +210,13 @@ BOOL ShouldCellsBeFullWidth(UITraitCollection* collection) {
   [super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
   [self.collectionUpdater updateMostVisitedForSize:size];
   [self.collectionView reloadData];
+
+  void (^alongsideBlock)(id<UIViewControllerTransitionCoordinatorContext>) =
+      ^(id<UIViewControllerTransitionCoordinatorContext> context) {
+        [self.headerCommandHandler
+            updateFakeOmniboxForScrollView:self.collectionView];
+      };
+  [coordinator animateAlongsideTransition:alongsideBlock completion:nil];
 }
 
 - (void)willTransitionToTraitCollection:(UITraitCollection*)newCollection