blink: Add backdrop-filter support

Source/core/style/StyleDifference.h

Index: Source/core/style/StyleDifference.h
diff --git a/Source/core/style/StyleDifference.h b/Source/core/style/StyleDifference.h
index 1d3e610ea4a1bfda53cf0220001923984fe2baac..14b261bd321ef367f7cb7ed39bee4df5c0689a9f 100644
--- a/Source/core/style/StyleDifference.h
+++ b/Source/core/style/StyleDifference.h
@@ -16,8 +16,10 @@ public:
         OpacityChanged = 1 << 1,
         ZIndexChanged = 1 << 2,
         FilterChanged = 1 << 3,
+        BackdropFilterChanged = 1 << 4,
         // The object needs to issue paint invalidations if it contains text or properties dependent on color (e.g., border or outline).
-        TextOrColorChanged = 1 << 4,
+        TextOrColorChanged = 1 << 5,
+        // If you add a value here, be sure to update the number of bits on m_propertySpecificDifferences.
     };
 
     StyleDifference()
@@ -74,6 +76,9 @@ public:
     bool filterChanged() const { return m_propertySpecificDifferences & FilterChanged; }
     void setFilterChanged() { m_propertySpecificDifferences |= FilterChanged; }
 
+    bool backdropFilterChanged() const { return m_propertySpecificDifferences & BackdropFilterChanged; }
+    void setBackdropFilterChanged() { m_propertySpecificDifferences |= BackdropFilterChanged; }
+
     bool textOrColorChanged() const { return m_propertySpecificDifferences & TextOrColorChanged; }
     void setTextOrColorChanged() { m_propertySpecificDifferences |= TextOrColorChanged; }
 
@@ -92,7 +97,7 @@ private:
     };
     unsigned m_layoutType : 2;
 
-    unsigned m_propertySpecificDifferences : 5;
+    unsigned m_propertySpecificDifferences : 6;
 };
 
 } // namespace blink