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Eliminates text rendering artifacts resulting from launching Chrome
browser with Windows Text Zoom enabled.

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Background
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The new Windows Text Zoom accessibility feature scales small text on
the screen by an amount in addition to normal DPI scaling. In
consultation with MS accessibility engineers, we have decided that
rather than doing complex and extensive scaling math in Chrome, we are
just going to have the browser scale additionally by that factor.
Chrome now scales dynamically with the zoom factor.

When we read default system fonts (such as those used by the
views::Label class - used by tabs, menu items, bookmarks, etc.), Windows
reports the logical size of the font. This does not take DPI into
account, but it *does* take the Windows Text Zoom amount into account
(for backwards-compatibility with apps that don't read it directly).

When the UI renders the text, it scales by the overall browser scale
factor (which includes both DPI and Windows Text Zoom). So effectively,
if the Text Zoom is set before Chrome starts, all system-default text
ends up scaled *twice*.

Correct text size (current behavior only if Text Zoom is changed *after*
launching Chrome):
 Text Scale 100% 150% 200%
DPI 100%     12   18   24
DPI 150%     18   27   36
DPI 200%     24   36   48

Current text size if Text Zoom is enabled prior to launching Chrome:
 Text Scale 100% 150% 200%
DPI 100%     12   27   48
DPI 150%     18   39   72
DPI 200%     24   54   96

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Patch Details
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This change captures the situations in which we ask Windows for a system
font (for menus and captions), and removes the additional scaling done by
the OS, since we are already taking this into account when rendering
text.

We already apply scaling for localization in most of these places for
similar reasons, so there is a precedent.

Chrome still scales appropriately when Text Scale Factor or DPI is set
prior to Chrome launch or changed dynamically while Chrome is running.

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Follow-Ups
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We call GetNonClientMetrics() in a number of plces, and use LOGFONT*
structs as well. These are Windows implementation details and should
ideally be hidden away from browser code. We should consolidate to a
single cache of system fonts, which will internally ensure that the fonts
are scaled appropriately (preferably in gfx::PlatformFontWin or similar).

Bug: 866513
Change-Id: Ideb248e2f196bb93d46a3f60780c68cf31446097
Reviewed-on: https://chromium-review.googlesource.com/1235313
Commit-Queue: Dana Fried <dfried@chromium.org>
Reviewed-by: Robert Liao <robliao@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593732}