Enable new multicol for testing and experimental web platform features.

Source/core/layout/LayoutBlockFlow.cpp

Index: Source/core/layout/LayoutBlockFlow.cpp
diff --git a/Source/core/layout/LayoutBlockFlow.cpp b/Source/core/layout/LayoutBlockFlow.cpp
index 8669124ed8f2ef292fbca9a26c3e806ace4d1d6d..f01ea47e8949a20fad5add014c87589eabcdff00 100644
--- a/Source/core/layout/LayoutBlockFlow.cpp
+++ b/Source/core/layout/LayoutBlockFlow.cpp
@@ -49,6 +49,7 @@
 #include "core/paint/BlockFlowPainter.h"
 #include "core/paint/DeprecatedPaintLayer.h"
 #include "core/paint/LayoutObjectDrawingRecorder.h"
+#include "platform/RuntimeEnabledFeatures.h"
 #include "platform/geometry/TransformState.h"
 #include "platform/graphics/paint/ClipRecorderStack.h"
 #include "platform/text/BidiTextRun.h"
@@ -3070,7 +3071,7 @@ LayoutMultiColumnFlowThread* LayoutBlockFlow::createMultiColumnFlowThread(FlowTh
 
 void LayoutBlockFlow::createOrDestroyMultiColumnFlowThreadIfNeeded(const LayoutStyle* oldStyle)
 {
-    if (!document().regionBasedColumnsEnabled())
+    if (!RuntimeEnabledFeatures::regionBasedColumnsEnabled())
         return;
 
     // Paged overflow trumps multicol in this implementation. Ideally, it should be possible to have