Assigning to avi@ for Q1 Mac work.

Tabs are actually supposed to animate straight up.

+helenepark@ to confirm.

Let me phrase it this way. In LTR mode and Chrome today, tabs animate straight up. If they're not supposed to, Chrome has been broken for a very very long time.

I added helenepark@ to get confirmation of the correct behavior. If you're going to make a change, I just want to make sure it's the right one. 

Yes, the form of the tab should be created along the X-axis, as opposed to straight up along the Y-axis.

Here is a deck with more information
https://docs.google.com/presentation/d/1bSakHoEHo14fVaPSdNBD2uTcuUPuN7zxnnJSq6dkXb4/edit#slide=id.g1bf2ae8936_0_51

Helene, Jayson:

This bug is about the RTL behavior not matching the LTR behavior. I am fixing that, so that the RTL behavior is a pure mirror of the LTR behavior.

If you want to change the Cocoa tabstrip behavior to match Views, please file a bug for that. Jayson, we'd need to decide a priority given the adoption schedule of MacViews.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d1065b766d40d754475f9270eea5ed3ce295e81b

commit d1065b766d40d754475f9270eea5ed3ce295e81b
Author: avi <avi@chromium.org>
Date: Thu Feb 09 04:31:58 2017

Do RTL tabstrip transforms before animating tabs.

BUG= 672873 
TEST=as in bug

Review-Url: https://codereview.chromium.org/2680203004
Cr-Commit-Position: refs/heads/master@{#449199}

[modify] https://crrev.com/d1065b766d40d754475f9270eea5ed3ce295e81b/chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm

> This bug is about the RTL behavior not matching the LTR behavior. I am fixing that, so that the RTL behavior is a pure mirror of the LTR behavior.

I'm not sure I agree with changing the RTL behavior to match LTR when LTR is wrong - that was my main point. In the end, it's wasted effort because while consistent, it is still wrong.

I think  issue 681234  is tracking the Cocoa tabstrip behavior to match Views.

The fix here wasn't to adjust the animation. I fixed a broken coordinate transform that affected other issues (e.g. tab overflow), and incidentally messed up the animation. I didn't touch the animation code. It wasn't an issue of "while you're in here"; I never was in there in the first place.

You are asking me to change the animation code. That's a much bigger deal than fixing a broken coordinate transform. I don't have a problem adjusting the animation, however... this is a case of two issues appearing to be related visually but underneath having two very different causes.

I fixed the cause of this, and that was this bug. If we want to change the animation, file a new bug for that and we can address it.

Mehmet: yes, that's exactly the bug tracking the animation issue. Thank you for finding it.