Remove a DCHECK when snapshotting the toolbar for stack view.

The DCHECK was added defensively for the developers to make sure that
the animation looks fine if one day it's hit. I've checked that the
animation looks fine and nothing jumps around, hence removing it.

to the tab switcher and rotating the phone, then choosing one of the
tabs. The toolbar should be animated correctly. Specifically test
iPhone X.

Bug: 788742
Test: Enable Tab switcher presents BVC experimental flag. Try going
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Ib906b4aaa1ac2b2e7eefa3f82931fa59a4dd3ac8
Reviewed-on: https://chromium-review.googlesource.com/806335Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521402}

ios/chrome/browser/ui/toolbar/legacy_toolbar_coordinator.mm

@@ -213,12 +213,6 @@
 
 - (UIView*)snapshotForStackViewWithWidth:(CGFloat)width
                           safeAreaInsets:(UIEdgeInsets)safeAreaInsets {
-  // The snapshotted view must not be in the view hierarchy, because the code
-  // below temporarily changes the frames of views in order to take the snapshot
-  // in simulated target frame. The frames will be returned to normal after the
-  // snapshot is taken.
-  DCHECK(self.toolbarViewController.view.window == nil);
-
   CGRect oldFrame = self.toolbarViewController.view.superview.frame;
   CGRect newFrame = oldFrame;
   newFrame.size.width = width;