Tested the same on win8.1 chrome version 51.0.2694.1 canary - observed that tab-size:4 is taken for each tab character as shown in the screenshot

Could you please attach a screenshot/screencast for better understanding of the issue 

Deleted: 598632.png 302 KB

	598632.png 302 KB View Download

This bug is about the "View Source" view in Chromium, not platform support for CSS's tab-size. Sorry if that wasn't clear.

In the attached screenshot, the indentation in lines 4-8 is a single "tab" character, which is rendered with a width equivalent to 8 spaces. I'm suggesting using a width of 4 spaces. (If by chance that view is built in HTML/XML and CSS, that could be as simple as adding tab-size:4 to its stylesheet.)

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	View Source with tab size of 8 spaces.png 32.7 KB View Download

The old bug ticket was https://bugs.chromium.org/p/chromium/issues/detail?id=598632.

I'll do a compile and see if setting tab-size in the CSS itself works. It does work when changing it in DevTools, so I don't see why the original patch wouldn't work.

I can confirm that `view-source` is using 8 spaces instead of 4 for tab characters.

If the `tab-size` value for `view-source:` URLs is changed, it should be changed to `2` rather than `4` to match the DevTools DOM view indentation.

Not sure about the `2` value. In DevTools:

- "Elements > Edit as HTML" uses `4`.
- "Sources" uses `4` as well.

Do you advocate changing it across the board?

- "sources" is configurable in settings, 4 is default.
- Edit as HTML in Elements does an actual tab character.

2 is how the Elements panel itself represents indentation of nodes. So going with 2 is the best choice to align with that.

CL [1] is open for the update to 2 spaces for tabs.

[1] https://codereview.chromium.org/1845923002

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0a353ab8c75241ef2e1101bcf5e2e23ae32a1fbf

commit 0a353ab8c75241ef2e1101bcf5e2e23ae32a1fbf
Author: jonathan.garbee <jonathan.garbee@chromium.org>
Date: Mon Apr 04 14:57:06 2016

4 spaces for tab size in view source.

BUG= 598632 

Review URL: https://codereview.chromium.org/1845923002

Cr-Commit-Position: refs/heads/master@{#384906}

[modify] https://crrev.com/0a353ab8c75241ef2e1101bcf5e2e23ae32a1fbf/third_party/WebKit/Source/core/css/view-source.css

Re: comment #7:

> "Elements > Edit as HTML" uses `4`.

No, it uses whatever the source document is using (i.e. the `innerHTML`). The document you were testing it on must have used 4-space indents, but that’s not true for every HTML document on the web.

Ah, good to know Mathias. Thanks for clarifying that.

Just verified the fix is working in Version 51.0.2702.0. So it should be going out to Beta and Stable channels with M51.

>> "Elements > Edit as HTML" uses `4`.

> No, it uses whatever the source document is using (i.e. the `innerHTML`)

For the record, I wasn’t talking about the indentation style in “Edit as HTML”. I only meant that when “Edit as HTML” editor view contains literal tabulation characters (U+0009), then each of those characters is rendered as having the same width as 4 space (U+0020) characters (whether that’s implemented using `tab-size:4` or not, I don’t know).