[New Multicolumn] Faster and more direct RenderMultiColumnSet::multiColumnFlowThread().

Source/core/rendering/RenderMultiColumnSet.h

Index: Source/core/rendering/RenderMultiColumnSet.h
diff --git a/Source/core/rendering/RenderMultiColumnSet.h b/Source/core/rendering/RenderMultiColumnSet.h
index 98a68bfa14b2d9323c551de085dfee272016efee..29ec4f252dc003051e58f5c8308fd7155175199c 100644
--- a/Source/core/rendering/RenderMultiColumnSet.h
+++ b/Source/core/rendering/RenderMultiColumnSet.h
@@ -27,6 +27,7 @@
 #ifndef RenderMultiColumnSet_h
 #define RenderMultiColumnSet_h
 
+#include "core/rendering/RenderMultiColumnFlowThread.h"
 #include "core/rendering/RenderRegionSet.h"
 #include "wtf/Vector.h"
 
@@ -56,7 +57,13 @@ public:
     virtual bool isRenderMultiColumnSet() const OVERRIDE { return true; }
 
     RenderBlockFlow* multiColumnBlockFlow() const { return toRenderBlockFlow(parent()); }
-    RenderMultiColumnFlowThread* multiColumnFlowThread() const { return multiColumnBlockFlow()->multiColumnFlowThread(); }
+    RenderMultiColumnFlowThread* multiColumnFlowThread() const
+    {
+#ifndef NDEBUG
+        ASSERT_WITH_SECURITY_IMPLICATION(!flowThread() || flowThread()->isRenderMultiColumnFlowThread());

[ojan, 2014/04/30 17:31:28]

Nit: I don't think this does anything different than plain ASSERT in debug
builds. The point of ASSERT_WITH_SECURITY_IMPLICATION is that we can run release
builds with these asserts turned on for clusterfuzz so that we find these
asserts in release builds.

I guess there's no harm in making it an ASSERT_WITH_SECURITY_IMPLICATION. If
this really has security implications, then I'd say you should remove the NDEBUG
check and do this in release builds. The code should all get stripped in
non-clusterfuzz release builds anyways. That way clusterfuzz will find code that
hits this assert.

+#endif // NDEBUG
+        return static_cast<RenderMultiColumnFlowThread*>(flowThread());
+    }
 
     RenderMultiColumnSet* nextSiblingMultiColumnSet() const;