Getting the following build error which was caused by 270501@main. Sadly, 270504@main did not suffice.

In file included from /Users/antoine/Builds/Release-iphonesimulator/DerivedSources/WebKit/unified-sources/UnifiedSource62-mm.mm:6:
/Users/antoine/Code/safari/OpenSource/Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.mm:204:68: error: receiver 'UIColor' is a forward class and corresponding @interface may not exist [-Werror,-Wreceiver-forward-class]
    context.fillRect(clipRect, WebCore::roundAndClampToSRGBALossy([WebCore::CocoaColor grayColor].CGColor));
In file included from /Users/antoine/Builds/Release-iphonesimulator/DerivedSources/WebKit/unified-sources/UnifiedSource62-mm.mm:6:
In file included from /Users/antoine/Code/safari/OpenSource/Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.mm:36:
/Users/antoine/Builds/Release-iphonesimulator/WebCore.framework/PrivateHeaders/ColorCocoa.h:35:12: note: forward declaration of class here
OBJC_CLASS UIColor;
In file included from /Users/antoine/Builds/Release-iphonesimulator/DerivedSources/WebKit/unified-sources/UnifiedSource62-mm.mm:6:
/Users/antoine/Code/safari/OpenSource/Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.mm:204:88: error: class method '+grayColor' not found (return type defaults to 'id') [-Werror,-Wobjc-method-access]
    context.fillRect(clipRect, WebCore::roundAndClampToSRGBALossy([WebCore::CocoaColor grayColor].CGColor));
/Users/antoine/Code/safari/OpenSource/Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.mm:204:99: error: property 'CGColor' not found on object of type 'id'
    context.fillRect(clipRect, WebCore::roundAndClampToSRGBALossy([WebCore::CocoaColor grayColor].CGColor));
3 errors generated.