[layoutng] Add a base class for layout algorithms

third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.h

Index: third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.h
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.h b/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.h
index 9f5f30ba0d9d7196379b3dc6087748b52cc96edf..0f92ad1b29a26372479cc7c0bbe29d4435ac6866 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.h
+++ b/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.h
@@ -7,6 +7,7 @@
 
 #include "core/CoreExport.h"
 #include "core/layout/ng/ng_box.h"
+#include "core/layout/ng/ng_layout_algorithm.h"
 #include "wtf/RefPtr.h"
 
 namespace blink {
@@ -17,7 +18,7 @@ class NGFragment;
 
 // A class for general block layout (e.g. a <div> with no special style).
 // Lays out the children in sequence.
-class CORE_EXPORT NGBlockLayoutAlgorithm {
+class CORE_EXPORT NGBlockLayoutAlgorithm : public NGLayoutAlgorithm {
  public:
   NGBlockLayoutAlgorithm(PassRefPtr<const ComputedStyle>, NGBox);
 
@@ -26,7 +27,7 @@ class CORE_EXPORT NGBlockLayoutAlgorithm {
   // resulting layout information.
   // This function can not be const because for interruptible layout, we have
   // to be able to store state information.
-  NGFragment* layout(const NGConstraintSpace&);
+  NGFragment* layout(const NGConstraintSpace&) override;
 
  private:
   RefPtr<const ComputedStyle> m_style;