Are you sure this is a regression for gaia signin? I think that codepath is separate (SigninViewControllerDelegateViews is not a WebContentsDialogDelegate) and I don't think it ever worked differently.

WebContentsDialogDelegate does look like it has a clash between SetPreferredSize and CalculatePreferredSize (the latter no longer being called). Few dialogs actually use this codepath --- I think it's just some obscure email confirmation dialog and the cast dialog. How can I easily trigger the cast dialog? I think this patch[1] should fix it but haven't tested it.

[1] ConstrainedWebDialogDelegateViewViews

Thank you for taking a look! I'm assuming this [1] was the patch you meant to link, and yes, it does fix the issue. The dialog can be opened via the "Cast..." option in the hotdog menu or the right-click context menu.

No, I'm not sure whether it's a regression for the sign-in dialog.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/674179

um yes, copy pasta fail. Thanks for checking.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f094b59b055c5051242315be5e2bcdaff1068803

commit f094b59b055c5051242315be5e2bcdaff1068803
Author: Evan Stade <estade@chromium.org>
Date: Tue Sep 26 16:46:48 2017

Resize media router (cast) dialog when browser changes size.

Most of the lines of change in this patch are just from splitting 
the declaration and definition for ConstrainedWebDialogDelegateViewViews.
This entire file is a painful morass of similarly named classes that are
all defined inline.

Bug:  766774 
Change-Id: I4ebfece91d9398571232cf350a2dd27f117d88f4
Reviewed-on: https://chromium-review.googlesource.com/674179
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504397}
[modify] https://crrev.com/f094b59b055c5051242315be5e2bcdaff1068803/chrome/browser/ui/views/constrained_web_dialog_delegate_views.cc

Tested this issue on Windows 7, Mac OS 10.12.6 and Ubuntu 14.04 using the latest Canary and can observe that on selecting the cast option from the wrench menu and resizing the Chrome Window, the cast window is displayed as it is and it is not cropped or re-sized in Mac OS.
Whereas in Windows and Linux, the Cast window is getting cropped and no scroll bars are seen.

Attached is the screen casts for the same.

estade@ Can you please check and confirm if the fix is working as intended or no?

Thanks..

Deleted: 766774_Windows.webm 6.5 MB

	766774_Windows.webm 6.5 MB View Download

Deleted: 766774_Mac.webm 3.9 MB

	766774_Mac.webm 3.9 MB View Download

Takumi, could you verify? Thanks.

Verified on Win and Mac Canary. Thank you for the fix!