[tab_container] Hack-in fix for broken constraint on animation

Custom view controller transition animations must be designed
so as not to break constraints on the presented/dismissed VC's view.

This CL addresses a broken constraint due to the zoom animator.
The zoom animator will resize the VC's view to a small rect.
However, that rect is smaller in height than the sum of the
height constraints on the subviews of the tab_container.

This CL simply reduces the subview height constant. Since the
transition animation will likely change, there is no need to modify
the zoom animator at this time.

BUG=

Review-Url: https://codereview.chromium.org/2717133002
Cr-Commit-Position: refs/heads/master@{#453249}

ios/clean/chrome/browser/ui/tab/tab_container_view_controller.mm

@@ -17,7 +17,7 @@
 
 namespace {
 CGFloat kToolbarHeight = 44.0f;
-CGFloat kTabStripHeight = 200.0f;
+CGFloat kTabStripHeight = 90.0f;
 }
 
 @interface TabContainerViewController ()