Remove CSS_REGIONS compile flag from Blink.

Source/core/dom/NamedFlowCollection.cpp

Index: Source/core/dom/NamedFlowCollection.cpp
diff --git a/Source/core/dom/NamedFlowCollection.cpp b/Source/core/dom/NamedFlowCollection.cpp
index ef75c9309d73a75c2f9a69d768c68391b6cd66c5..ea888317daf13620d86b8b99605da9ef90b3620d 100644
--- a/Source/core/dom/NamedFlowCollection.cpp
+++ b/Source/core/dom/NamedFlowCollection.cpp
@@ -30,6 +30,7 @@
 #include "config.h"
 #include "core/dom/NamedFlowCollection.h"
 
+#include "RuntimeEnabledFeatures.h"
 #include "core/dom/DOMNamedFlowCollection.h"
 #include "core/dom/Document.h"
 #include "core/dom/NamedFlow.h"
@@ -43,6 +44,7 @@ namespace WebCore {
 NamedFlowCollection::NamedFlowCollection(Document* document)
     : ContextDestructionObserver(document)
 {
+    ASSERT(RuntimeEnabledFeatures::cssRegionsEnabled());
 }
 
 Vector<RefPtr<NamedFlow> > NamedFlowCollection::namedFlows()