CL: https://codereview.chromium.org/1759483005/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/60d08d73239ed483f80d19a34954560daac392e8

commit 60d08d73239ed483f80d19a34954560daac392e8
Author: estade <estade@chromium.org>
Date: Thu Mar 03 22:06:29 2016

[MD] turn on MD by default for desktop linux

BUG=505982, 591715 

Review URL: https://codereview.chromium.org/1759483005

Cr-Commit-Position: refs/heads/master@{#379107}

[modify] https://crrev.com/60d08d73239ed483f80d19a34954560daac392e8/ui/base/material_design/material_design_controller.cc

Should we consider merging this into M-50 beta branch?

No, it's intentional that we waited till after the branch.

This should have been blocked by  issue 595108  - Linux unable to disable MD with top-chome-md=non-material.  

See my comments on  bug 595108  for details.

A fix for  bug 595108  landed after the M-51 branch point. In M-51 command line can be used to switch the value of --top-chrome-md flag on Linux.

The flag only exists for testing and debugging, it's not intended for end users.

@estade C#9: Are you sure (not intended for end user's)?  
a) at least on Windows top-chrome-md has been available for sometime to preview the new UI, both as material and hybrid
b) top-chrome-md is a substantial change.  Don't we give users an option to turn it off if there are bugs/deficiencies?  At least until it's cooked?

refer to the disclaimer at the top of about:flags :)

@estade C#11 It still seems abrupt to jump from Linux Chrome 50 default non-material to M-51 MD, can't be disabled.