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 dfcebdc15f07bae306b16ed8f99c1a3684d8cde0..09391ed798e40c4d617d4c7d92dd5c6cf2aeedc3 100644
--- a/Source/core/layout/LayoutBlockFlow.cpp
+++ b/Source/core/layout/LayoutBlockFlow.cpp
@@ -52,6 +52,7 @@
 #include "core/paint/DeprecatedPaintLayer.h"
 #include "core/paint/LayoutObjectDrawingRecorder.h"
 #include "core/paint/PaintInfo.h"
+#include "platform/RuntimeEnabledFeatures.h"
 #include "platform/geometry/TransformState.h"
 #include "platform/text/BidiTextRun.h"
 
@@ -3102,7 +3103,7 @@ LayoutMultiColumnFlowThread* LayoutBlockFlow::createMultiColumnFlowThread(FlowTh
 
 void LayoutBlockFlow::createOrDestroyMultiColumnFlowThreadIfNeeded(const ComputedStyle* oldStyle)
 {
-    if (!document().regionBasedColumnsEnabled())
+    if (!RuntimeEnabledFeatures::regionBasedColumnsEnabled())
         return;
 
     // Paged overflow trumps multicol in this implementation. Ideally, it should be possible to have