Move tab grid's new tab button upwards when thumb strip is enabled.

The tab grid's new tab button is covered by the BVC when the tab grid is
visible and the thumb strip feature is enabled. Nudge the new tab button
by a distance equal to the height of the BVC that remains visible when
the tab grid is showing.

Bug: 1094335
Change-Id: I54d7aa20633e109cf41b6bfe46866cecb23584aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2487320
Commit-Queue: Roberto Moura <mouraroberto@google.com>
Auto-Submit: Roberto Moura <mouraroberto@google.com>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819450}

ios/chrome/browser/ui/tab_grid/tab_grid_bottom_toolbar.mm

@@ -4,8 +4,10 @@
 
 #import "ios/chrome/browser/ui/tab_grid/tab_grid_bottom_toolbar.h"
 
+#import "ios/chrome/browser/ui/tab_grid/grid/grid_constants.h"
 #import "ios/chrome/browser/ui/tab_grid/tab_grid_constants.h"
 #import "ios/chrome/browser/ui/tab_grid/tab_grid_new_tab_button.h"
+#import "ios/chrome/browser/ui/thumb_strip/thumb_strip_feature.h"
 #import "ios/chrome/browser/ui/util/uikit_ui_util.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
@@ -147,11 +149,15 @@
   _largeNewTabButton.translatesAutoresizingMaskIntoConstraints = NO;
   _largeNewTabButton.page = self.page;
 
+  CGFloat floatingButtonVerticalInset = kTabGridFloatingButtonVerticalInset;
+  if (IsThumbStripEnabled())
+    floatingButtonVerticalInset += kBVCHeightTabGrid;
+
   _floatingConstraints = @[
     [_largeNewTabButton.topAnchor constraintEqualToAnchor:self.topAnchor],
     [_largeNewTabButton.bottomAnchor
         constraintEqualToAnchor:self.safeAreaLayoutGuide.bottomAnchor
-                       constant:-kTabGridFloatingButtonVerticalInset],
+                       constant:-floatingButtonVerticalInset],
     [_largeNewTabButton.trailingAnchor
         constraintEqualToAnchor:self.trailingAnchor
                        constant:-kTabGridFloatingButtonHorizontalInset],