https://chromium-review.googlesource.com/c/chromium/src/+/943109 fix up.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e03b7d60c7611be9c5ca33faf00cada944c2bb02

commit e03b7d60c7611be9c5ca33faf00cada944c2bb02
Author: Dominik Röttsches <drott@chromium.org>
Date: Fri Mar 02 12:33:39 2018

Keep FreeType FontManager when applying variation parameters for CFF2

CFF2 fonts are initially instantiated using FreeType, but when applying
variation parameters, Blink attempted to switch back to CoreText. This
failed, since CoreText cannot instantiate those, leading to variation
axis values not being applied.

Extend format probing in FontCustomPlatformData to keep the original
SkFontMgr for the base_typeface_ that this font is originally
instantiated from.

Thanks to Laurence Penney (@lorp) for the report.

Bug:  815251 
Test: fast/text/variable-fonts/cff2-variations.html
Change-Id: I7d438788380c2f052fdf79b11c8145dce2721483
Reviewed-on: https://chromium-review.googlesource.com/943109
Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540502}
[add] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/LayoutTests/fast/text/variable-fonts/cff2-variations.html
[add] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/LayoutTests/platform/linux/fast/text/variable-fonts/cff2-variations-expected.png
[add] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/LayoutTests/platform/mac-mac10.10/fast/text/variable-fonts/cff2-variations-expected.png
[delete] https://crrev.com/1172c37b4ad4ed555b59a3010290988beee1eec1/third_party/WebKit/LayoutTests/platform/mac-mac10.11/fast/text/font-format-support-cbdt-sbix-cff2-vertical-expected.png
[modify] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/LayoutTests/platform/mac-mac10.12/fast/text/font-format-support-cbdt-sbix-cff2-expected.png
[modify] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/LayoutTests/platform/mac-mac10.12/fast/text/font-format-support-cbdt-sbix-cff2-vertical-expected.png
[add] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/LayoutTests/platform/mac-mac10.12/fast/text/variable-fonts/cff2-variations-expected.png
[modify] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/LayoutTests/platform/mac-retina/fast/text/font-format-support-cbdt-sbix-cff2-expected.png
[delete] https://crrev.com/1172c37b4ad4ed555b59a3010290988beee1eec1/third_party/WebKit/LayoutTests/platform/mac-retina/fast/text/font-format-support-cbdt-sbix-cff2-vertical-expected.png
[add] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/LayoutTests/platform/win/fast/text/variable-fonts/cff2-variations-expected.png
[add] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/LayoutTests/platform/win7/fast/text/variable-fonts/cff2-variations-expected.png
[modify] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/Source/platform/fonts/FontCustomPlatformData.cpp
[modify] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/Source/platform/fonts/WebFontTypefaceFactory.h
[modify] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/Source/platform/fonts/opentype/FontFormatCheck.cpp
[modify] https://crrev.com/e03b7d60c7611be9c5ca33faf00cada944c2bb02/third_party/WebKit/Source/platform/fonts/opentype/FontFormatCheck.h