Cleanup <static_cast>: Switch to toFoo for Accessibility Objects.

Source/core/accessibility/AccessibilityTableColumn.h

Index: Source/core/accessibility/AccessibilityTableColumn.h
diff --git a/Source/core/accessibility/AccessibilityTableColumn.h b/Source/core/accessibility/AccessibilityTableColumn.h
index 09de7ecab27c28c40214e26cd7d443739c06b421..bf0ffd3dacbfa6396d7c1bf73305935bf3954011 100644
--- a/Source/core/accessibility/AccessibilityTableColumn.h
+++ b/Source/core/accessibility/AccessibilityTableColumn.h
@@ -60,10 +60,26 @@ private:
     unsigned m_columnIndex;
     LayoutRect m_columnRect;
 
+    virtual bool isTableCol() const OVERRIDE { return true; }
     AccessibilityObject* headerObjectForSection(RenderTableSection*, bool thTagRequired);
     virtual bool computeAccessibilityIsIgnored() const OVERRIDE;
 };
 
+inline AccessibilityTableColumn* toAccessibilityTableColumn(AccessibilityObject* object)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isTableCol());
+    return static_cast<AccessibilityTableColumn*>(object);
+}
+
+inline const AccessibilityTableColumn* toAccessibilityTableColumn(const AccessibilityObject* object)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isTableCol());
+    return static_cast<const AccessibilityTableColumn*>(object);
+}
+
+// This will catch anyone doing an unnecessary cast.
+void toAccessibilityTableColumn(const AccessibilityTableColumn*);
+
 } // namespace WebCore
 
 #endif // AccessibilityTableColumn_h