The system header in question is 

..\..\..\..\win_toolchain\vs_files\3bc0ec615cf20ee342f3bc29bc991b5ad66d8d2c\win_sdk\Include\10.0.17134.0\shared\rpcndr.h(190,15):  note: expanded from macro 'small'

This bug is preventing me from landing patches. Can someone from Infra team please take a look? Thanks!

I'm not sure what infra is supposed to do here. Don't call your variables "small", for it conflicts with system headers.

There is already code that has "small" in it [1]. The new CL does not introduce any AFAICT.

[1] https://codesearch.chromium.org/chromium/src/cc/trees/layer_tree_host_pixeltest_scrollbars.cc?q=layer_tree_host_pixeltest_scrollbars.cc&sq=package:chromium&dr&l=67

Have you made sure you're still seeing this in a CL that doesn't add any includes to any .h files? If not, I'm guessing the additional .h files cause that header to be pulled in, causing the collision.

Auditing the includes is a good idea. The new CL adds a few includes:
- "base/optional.h"
- "ui/gfx/range/range_f.h"
- <algorithm>

I suspect the <algorithm> may potentially pull in some unrelated stuff. We can check this.

optional.h also includes <utility> and some other header that I can't remember now but saw when I checked earlier.

Actuall /ui/gfx/range/range.h is including <windows.h>, but I have no idea why!

That is a much more likely suspect. We should start with that.

(taking out of infra queue then)

Probably for the CHARRANGE typedef. We could add it to base/win/windows_types.h and include that instead, maybe that's enough.

(But I'd also rename the variable, else this is just a landmine for the next person to run into this unintentionally)

Removing from sheriff queue.

+brucedawson since this partially falls under the "include windows.h less" umbrella

Removing #include of windows.h from range.h is definitely the sane way forwards. If necessary it can include windows_types.h instead.

The master windows.h bug is crbug.com/796644

I've created crrev.com/c/1117739 which removes the #include of windows.h from range.h which should help. Let me know. Either way I'll try to land it since it is a (small) step in the right direction.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3c41dd4c6f6ab218366dbe4557910245e3f31bda

commit 3c41dd4c6f6ab218366dbe4557910245e3f31bda
Author: Bruce Dawson <brucedawson@chromium.org>
Date: Thu Jun 28 16:22:59 2018

Don't include Windows.h from range.h

Including Windows.h causes namespace pollution and build-time costs due
to the heavy use of macros and the large size of the headers. This
removes a #include of Windows.h from range.h that is currently causing
problems.

Bug:  855717 , 796644
Change-Id: I26abd068ed1c4a5ca65092258dd45ccd076c2b20
Reviewed-on: https://chromium-review.googlesource.com/1117739
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571155}
[modify] https://crrev.com/3c41dd4c6f6ab218366dbe4557910245e3f31bda/ui/gfx/range/range.h
[modify] https://crrev.com/3c41dd4c6f6ab218366dbe4557910245e3f31bda/ui/gfx/range/range_win.cc
[modify] https://crrev.com/3c41dd4c6f6ab218366dbe4557910245e3f31bda/ui/gfx/range/range_win_unittest.cc

Mass UI Triage.