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

No need to go via the parent block to get the flow thread.

Review URL: https://codereview.chromium.org/254883003

git-svn-id: svn://svn.chromium.org/blink/trunk@173025 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/rendering/RenderFlowThread.h

@@ -58,6 +58,7 @@ public:
     virtual ~RenderFlowThread() { };
 
     virtual bool isRenderFlowThread() const OVERRIDE FINAL { return true; }
+    virtual bool isRenderMultiColumnFlowThread() const { return false; }
 
     virtual void layout() OVERRIDE FINAL;
 

third_party/WebKit/Source/core/rendering/RenderMultiColumnFlowThread.h

@@ -56,6 +56,8 @@ public:
 
     static RenderMultiColumnFlowThread* createAnonymous(Document&, RenderStyle* parentStyle);
 
+    virtual bool isRenderMultiColumnFlowThread() const OVERRIDE FINAL { return true; }
+
     RenderBlockFlow* multiColumnBlockFlow() const { return toRenderBlockFlow(parent()); }
 
     RenderMultiColumnSet* firstMultiColumnSet() const;

third_party/WebKit/Source/core/rendering/RenderMultiColumnSet.cpp

@@ -261,7 +261,7 @@ void RenderMultiColumnSet::prepareForLayout()
     // Set box width.
     updateLogicalWidth();
 
-    if (multicolBlock->multiColumnFlowThread()->requiresBalancing()) {
+    if (multiColumnFlowThread()->requiresBalancing()) {
         // Set maximum column height. We will not stretch beyond this.
         m_maxColumnHeight = RenderFlowThread::maxLogicalHeight();
         if (!multicolStyle->logicalHeight().isAuto()) {
@@ -277,7 +277,7 @@ void RenderMultiColumnSet::prepareForLayout()
         m_maxColumnHeight = heightAdjustedForSetOffset(m_maxColumnHeight);
         m_computedColumnHeight = 0; // Restart balancing.
     } else {
-        setAndConstrainColumnHeight(heightAdjustedForSetOffset(multicolBlock->multiColumnFlowThread()->columnHeightAvailable()));
+        setAndConstrainColumnHeight(heightAdjustedForSetOffset(multiColumnFlowThread()->columnHeightAvailable()));
     }
 
     clearForcedBreaks();

third_party/WebKit/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 +57,11 @@ public:
     virtual bool isRenderMultiColumnSet() const OVERRIDE { return true; }
 
     RenderBlockFlow* multiColumnBlockFlow() const { return toRenderBlockFlow(parent()); }
-    RenderMultiColumnFlowThread* multiColumnFlowThread() const { return multiColumnBlockFlow()->multiColumnFlowThread(); }
+    RenderMultiColumnFlowThread* multiColumnFlowThread() const
+    {
+        ASSERT_WITH_SECURITY_IMPLICATION(!flowThread() || flowThread()->isRenderMultiColumnFlowThread());
+        return static_cast<RenderMultiColumnFlowThread*>(flowThread());
+    }
 
     RenderMultiColumnSet* nextSiblingMultiColumnSet() const;