[iOS][Thumb Strip] Use constants to calculate thumb strip height

Bug: 1123048
Change-Id: Ie24d51180a741fecf06e03da908cfb6042de087f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2614781Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Robbie Gibson <rkgibson@google.com>
Cr-Commit-Position: refs/heads/master@{#841098}

ios/chrome/browser/ui/thumb_strip/thumb_strip_coordinator.mm

@@ -15,8 +15,10 @@
 
 namespace {
 // Height of the view that is revealed. The thumb strip has a height equal to a
-// small grid cell + edge insets (top and bottm) from thumb strip layout.
-const CGFloat kThumbStripHeight = 168.0f + 22.0f + 22.0f;
+// small grid cell + edge insets (top and bottom) from thumb strip layout.
+const CGFloat kThumbStripHeight =
+    kGridCellSizeSmall.height +
+    2 * kGridLayoutLineSpacingCompactCompactLimitedWidth;
 }  // namespace
 
 @interface ThumbStripCoordinator ()