[mac] Enable scaled cursors

Reviewed by Dean Jackson.

Source/JavaScriptCore: 

* Configurations/FeatureDefines.xcconfig:

Source/WebCore: 

Not much is required to get this turned on. We just need the feature to be 
defined, and we need to initialize m_imageScaleFactor in the Cursor constructors.

* Configurations/FeatureDefines.xcconfig:
* platform/mac/CursorMac.mm:
(WebCore::Cursor::Cursor):
(WebCore::Cursor::operator=):

Source/WebKit/mac: 

* Configurations/FeatureDefines.xcconfig:

Source/WebKit2: 

* Configurations/FeatureDefines.xcconfig:

LayoutTests: 

Un-skip these tests now that the feature is enabled.
* platform/mac/TestExpectations:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@138069 268f45cc-cd09-0410-ab3c-d52691b4dbfc