Unify platformWidthForGlyph across OS X and iOS

Unify platformWidthForGlyph across OS X and iOS
https://bugs.webkit.org/show_bug.cgi?id=132036

Reviewed by Darin Adler.

This patch creates on shared SimpleFontData::platformWidthForGlyph() function for both OS X and iOS.

No new tests are necessary because there should be no behavior changes.

* platform/graphics/SimpleFontData.h: Signatures for two helper functions
* platform/graphics/ios/SimpleFontDataIOS.mm: Replace iOS implementation of platformWidthForGlyph() with
implementations of only the two helper functions
(WebCore::SimpleFontData::getRenderingStyle): Compute style argument to CGFontGetGlyphAdvancesForStyle()
(WebCore::SimpleFontData::advanceForColorBitmapFont): iOS doesn't have color bitmap fonts
(WebCore::SimpleFontData::platformWidthForGlyph): Deleted.
* platform/graphics/mac/SimpleFontDataMac.mm:
(WebCore::SimpleFontData::getRenderingStyle): Compute style argument to CGFontGetGlyphAdvancesForStyle()
(WebCore::SimpleFontData::advanceForColorBitmapFont): Use [NSFont advancementForGlyph] to compute the advance
(WebCore::hasCustomTracking): Removed #if
(WebCore::isEmoji): Only relevant on iOS
(WebCore::SimpleFontData::platformWidthForGlyph): Shared implementation. Calls helper functions.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@167773 268f45cc-cd09-0410-ab3c-d52691b4dbfc