[WinCairo] Make it easier to enable/disable GStreamer.

[WinCairo] Make it easier to enable/disable GStreamer.
https://bugs.webkit.org/show_bug.cgi?id=135766

Patch by peavo@outlook.com <peavo@outlook.com> on 2014-09-15
Reviewed by Brent Fulgham.

Make it possible to enable/disable GStreamer by editing the new user macro ENABLE_GSTREAMER_WINCAIRO.

Source/WebCore:

* WebCore.vcxproj/WebCoreDebugWinCairo.props: Import GStreamer property file.
* WebCore.vcxproj/WebCoreReleaseWinCairo.props: Ditto.

Source/WebKit:

* WebKit.vcxproj/WebKit/WebKitDebugWinCairo.props: Import GStreamer property file.
* WebKit.vcxproj/WebKit/WebKitReleaseWinCairo.props: Ditto.

Source/WTF:

* WTF.vcxproj/WTFDebugWinCairo.props: Import GStreamer property file.
* WTF.vcxproj/WTFReleaseWinCairo.props: Ditto.
* wtf/Platform.h: Enable GStreamer if ENABLE(GSTREAMER_WINCAIRO) is true, otherwise use Media Foundation.

Tools:

* WinLauncher/WinMain.cpp: Compile fix when GStreamer is enabled.

WebKitLibraries:

* win/tools/vsprops/GStreamerCommon.props: Add user macro ENABLE_GSTREAMER_WINCAIRO.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@173616 268f45cc-cd09-0410-ab3c-d52691b4dbfc