Implement 'will-change' parsing

Source/core/frame/UseCounter.cpp

Index: Source/core/frame/UseCounter.cpp
diff --git a/Source/core/frame/UseCounter.cpp b/Source/core/frame/UseCounter.cpp
index 1051e36d1d1ee138b4c736735fd852e313e62708..a768ccf6748bebe2451b59ec969b34fc981d07e0 100644
--- a/Source/core/frame/UseCounter.cpp
+++ b/Source/core/frame/UseCounter.cpp
@@ -497,6 +497,7 @@ int UseCounter::mapCSSPropertyIdToCSSSampleIdForHistogram(int id)
     case CSSPropertyTouchActionDelay: return 442;
     case CSSPropertyJustifySelf: return 443;
     case CSSPropertyScrollBehavior: return 444;
+    case CSSPropertyWillChange: return 445;
 
     // Add new features above this line (don't change the assigned numbers of the existing
     // items) and update maximumCSSSampleId() with the new maximum value.
@@ -516,7 +517,7 @@ int UseCounter::mapCSSPropertyIdToCSSSampleIdForHistogram(int id)
     return 0;
 }
 
-static int maximumCSSSampleId() { return 444; }
+static int maximumCSSSampleId() { return 445; }
 
 UseCounter::UseCounter()
 {