Don't include LayoutObject-derived headers where not needed.

third_party/WebKit/Source/core/layout/FlexibleBoxAlgorithm.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 14 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef FlexibleBoxAlgorithm_h
 #define FlexibleBoxAlgorithm_h
 
 #include "core/CoreExport.h"
-#include "core/layout/LayoutBox.h"
 #include "core/layout/OrderIterator.h"
+#include "core/style/ComputedStyle.h"
+#include "platform/LayoutUnit.h"
 #include "wtf/Noncopyable.h"
+#include "wtf/Vector.h"
 
 namespace blink {
 
+class LayoutBox;
+
 class FlexItem {
  public:
   FlexItem(LayoutBox*,
            LayoutUnit flexBaseContentSize,
            LayoutUnit hypotheticalMainContentSize,
            LayoutUnit mainAxisBorderAndPadding,
            LayoutUnit mainAxisMargin);
 
   LayoutUnit hypotheticalMainAxisMarginBoxSize() const {
     return hypotheticalMainContentSize + mainAxisBorderAndPadding +
@@ skipping 39 matching lines @@
   bool isMultiline() const { return m_style->flexWrap() != FlexNoWrap; }
 
   const ComputedStyle* m_style;
   LayoutUnit m_lineBreakLength;
   const Vector<FlexItem>& m_allItems;
 };
 
 }  // namespace blink
 
 #endif  // FlexibleBoxAlgorithm_h