Add operator<< to StyleDifference for debug logging.

third_party/WebKit/Source/core/style/StyleDifference.h

 // Copyright 2014 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 StyleDifference_h
 #define StyleDifference_h
 
+#include <iosfwd>
+#include "core/CoreExport.h"
 #include "wtf/Allocator.h"
 #include "wtf/Assertions.h"
 
 namespace blink {
 
 class StyleDifference {
   STACK_ALLOCATED();
 
  public:
   enum PropertyDifference {
     TransformChanged = 1 << 0,
     OpacityChanged = 1 << 1,
     ZIndexChanged = 1 << 2,
     FilterChanged = 1 << 3,
     BackdropFilterChanged = 1 << 4,
     CSSClipChanged = 1 << 5,
     // The object needs to issue paint invalidations if it is affected by text
     // decorations or properties dependent on color (e.g., border or outline).
     TextDecorationOrColorChanged = 1 << 6,
-    // If you add a value here, be sure to update the number of bits on
-    // m_propertySpecificDifferences.
+    // If you add a value here, be sure to update kPropertyDifferenceCount.
   };
 
   StyleDifference()
       : m_paintInvalidationType(NoPaintInvalidation),
         m_layoutType(NoLayout),
         m_recomputeOverflow(false),
         m_propertySpecificDifferences(0),
         m_scrollAnchorDisablingPropertyChanged(false) {}
 
   bool hasDifference() const {
@@ skipping 93 matching lines @@
   }
 
   bool scrollAnchorDisablingPropertyChanged() const {
     return m_scrollAnchorDisablingPropertyChanged;
   }
   void setScrollAnchorDisablingPropertyChanged() {
     m_scrollAnchorDisablingPropertyChanged = true;
   }
 
  private:
+  static constexpr int kPropertyDifferenceCount = 7;
+
+  friend CORE_EXPORT std::ostream& operator<<(std::ostream&,
+                                              const StyleDifference&);
+
   enum PaintInvalidationType {
     NoPaintInvalidation,
     PaintInvalidationObject,
     PaintInvalidationSubtree,
   };
   unsigned m_paintInvalidationType : 2;
 
   enum LayoutType { NoLayout = 0, PositionedMovement, FullLayout };
   unsigned m_layoutType : 2;
   unsigned m_recomputeOverflow : 1;
-  unsigned m_propertySpecificDifferences : 7;
+  unsigned m_propertySpecificDifferences : kPropertyDifferenceCount;
   unsigned m_scrollAnchorDisablingPropertyChanged : 1;
 };
 
+CORE_EXPORT std::ostream& operator<<(std::ostream&, const StyleDifference&);
+
 }  // namespace blink
 
 #endif  // StyleDifference_h