Implement white-space property(pre)

[deokjinkim]

In order to support line-break by new-line character,
Fist, calculate new-line character's position.(fn flush_clump_to_list)
Second, split box(which includes new-line character) and do line-break.(fn scan_for_lines)

[hoppipolla-critic-bot]

Critic review: https://critic.hoppipolla.co.uk/r/562

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Warning

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[deokjinkim]

@pcwalton r?

[metajack]

I pointed out some nits and code duplication, but I think this is a sub-optimal solution.

Creating line break boxes looks like it works, but really we should not create these fake boxes which are only used to signal the line breaks. Instead, I think scan_for_lines should handle this logic.

Basically the idea is that the the white-space: normal mode tries to append each box to the line box. In white-space: pre mode, it should instead just make each box into its own line box.

When white-space: pre-wrap and other modes are added later, scan_for_lines can do a mixture of the things.

This seems like it makes the logic much simpler.

Also, I think it's ok that we compute newline locations in the text transforming function, but I'm less sure about where we should actually break the text runs. I think what you're doing now is probably useful, since we know it will need to be broken in those spots in all pre modes. Those might get broken more later.

[deokjinkim]

@metajack, r?

Thank you for your kind review~!!
I revised code for white-space(pre).
In order to support line-break by new-line character,
Fist, calculate new-line character's position.(fn flush_clump_to_list)
Second, split box(which includes new-line character) and do line-break.(fn scan_for_lines)

[deokjinkim]

I modified comment(main/layout/inline.rs).
@metajack r?

[deokjinkim]

@metajack I have same problem with aydinkim([servo] fix option order of make servo (#1539)). I don't know why this build error is occurred.