Add support for 8 bit TextRuns on Chromium Linux & Mac

Add support for 8 bit TextRuns on Chromium Linux & Mac
https://bugs.webkit.org/show_bug.cgi?id=99393

Reviewed by Eric Seidel.

Source/WebCore:

Adding support for 8 bit TextRuns for Mac and Linux Chromium. To accomplish this,
8 bit text runs are upconverted to 16 bit in the complex text path during string
normalization, as HarfBuzz operates on UChars.

Windows has platfom assumptions that TextRuns are 16 bit that need to be addressed
before enabling this optimization.

No new tests. No change in behavior.

(WebCore::HarfBuzzShaperBase::setNormalizedBuffer):
* platform/graphics/harfbuzz/HarfBuzzShaperBase.h:
* platform/graphics/harfbuzz/HarfBuzzShaper.cpp:
(WebCore::normalizeCharacters):
(WebCore::HarfBuzzShaper::HarfBuzzShaper):

Source/WebKit/chromium:

Enabling 8 bit text runs for Linux and Mac platforms.

* features.gypi:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@144646 268f45cc-cd09-0410-ab3c-d52691b4dbfc