Combine 2 exclusions in Layout Opportunity Tree if they shadow each other

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NGExclusion_h
 #define NGExclusion_h
 
 #include "core/CoreExport.h"
 #include "core/layout/ng/geometry/ng_logical_rect.h"
 #include "wtf/Vector.h"
@@ skipping 13 matching lines @@
     kFloatRight = 2
   };
 
   // Rectangle in logical coordinates the represents this exclusion.
   NGLogicalRect rect;
 
   // Type of this exclusion.
   Type type;
 
   bool operator==(const NGExclusion& other) const;
+
   String ToString() const;
+
+  // Tries to combine the current exclusion with {@code other} exclusion and
+  // returns true if successful.
+  // We can combine 2 exclusions if they
+  // - adjoining to each other and have the same exclusion type
+  // - {@code other} exclusion shadows the current one.
+  //   That's because it's not allowed to position anything in the shadowed
+  //   area.
+  //
+  //   Example:
+  //   <div id="SS" style="float: left; height: 10px; width: 10px"></div>
+  //   <div id="BB" style="float: left; height: 20px; width: 20px"></div>
+  //   +----------------+
+  //   |SSBB
+  //   |**BB
+  //   We combine SS and BB exclusions including the shadowed area (**).
+  bool MaybeCombineWith(const NGExclusion& other);
 };
 
 CORE_EXPORT std::ostream& operator<<(std::ostream&, const NGExclusion&);
 
 struct CORE_EXPORT NGExclusions {
   NGExclusions();
   NGExclusions(const NGExclusions& other);
 
   Vector<std::unique_ptr<const NGExclusion>> storage;
 
   // Last left/right float exclusions are used to enforce the top edge alignment
   // rule for floats and for the support of CSS "clear" property.
   const NGExclusion* last_left_float;   // Owned by storage.
   const NGExclusion* last_right_float;  // Owned by storage.
 
   NGExclusions& operator=(const NGExclusions& other);
 
   void Add(const NGExclusion& exclusion);
 };
 
 }  // namespace blink
 
 #endif  // NGExclusion_h