Add "customPropertiesApplied" metric to StyleResolverStats.

third_party/WebKit/Source/core/css/resolver/StyleResolverStats.cpp

Index: third_party/WebKit/Source/core/css/resolver/StyleResolverStats.cpp
diff --git a/third_party/WebKit/Source/core/css/resolver/StyleResolverStats.cpp b/third_party/WebKit/Source/core/css/resolver/StyleResolverStats.cpp
index a88e18b7b4e6b4e8ffef430640274708593dc92e..74c719b29d1e30f7c90e1f860849a1dcf1cf7713 100644
--- a/third_party/WebKit/Source/core/css/resolver/StyleResolverStats.cpp
+++ b/third_party/WebKit/Source/core/css/resolver/StyleResolverStats.cpp
@@ -56,6 +56,7 @@ void StyleResolverStats::reset() {
   pseudoElementsStyled = 0;
   baseStylesUsed = 0;
   independentInheritedStylesPropagated = 0;
+  customPropertiesApplied = 0;
 }
 
 bool StyleResolverStats::allCountersEnabled() const {
@@ -95,6 +96,7 @@ std::unique_ptr<TracedValue> StyleResolverStats::toTracedValue() const {
   tracedValue->setInteger("baseStylesUsed", baseStylesUsed);
   tracedValue->setInteger("independentInheritedStylesPropagated",
                           independentInheritedStylesPropagated);
+  tracedValue->setInteger("customPropertiesApplied", customPropertiesApplied);
   return tracedValue;
 }