Move ENABLE macros for WebCore out from Platform.h
https://bugs.webkit.org/show_bug.cgi?id=105735

Source/WebKit/chromium:

Move the chromium specific WebCore ENABLE macro definitions
from Platform.h to features.gypi.

Patch by Laszlo Gombos <l.gombos@samsung.com> on 2013-02-18
Reviewed by Darin Adler and Benjamin Poulain.

* features.gypi: Set ENABLE_SUBPIXEL_LAYOUT to 1.

Source/WTF:

Patch by Laszlo Gombos <l.gombos@samsung.com> on 2013-02-18
Reviewed by Darin Adler and Benjamin Poulain.

Introduce FeatureDefines.h by combining the existing rules from
Platform.h and adding new rules for all the ENABLE flags that are
listed in the FeatureFlags wiki.

The new rules are not used at the moment by any ports
as the port specific build systems already define these flags
so the !defined() guard will prevent redefinition of the macros.

* GNUmakefile.list.am: Add FeatureDefines.h.
* WTF.gypi: Ditto.
* WTF.pro: Ditto.
* WTF.vcproj/WTF.vcproj: Ditto.
* WTF.xcodeproj/project.pbxproj: Ditto.
* wtf/CMakeLists.txt: Ditto.
* wtf/FeatureDefines.h: Added.
* wtf/Platform.h: Move macro definitions to FeatureDefines.h.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143211 268f45cc-cd09-0410-ab3c-d52691b4dbfc