clang/win: Work around in-class initializer bug.

Source/core/css/resolver/MatchResult.cpp

Index: Source/core/css/resolver/MatchResult.cpp
diff --git a/Source/core/css/resolver/MatchResult.cpp b/Source/core/css/resolver/MatchResult.cpp
index 933c37e43f0cc8eb9d49d07acfac153ac1897bfa..347e6ca44a52248122f4ac420c504c067c275de0 100644
--- a/Source/core/css/resolver/MatchResult.cpp
+++ b/Source/core/css/resolver/MatchResult.cpp
@@ -48,6 +48,9 @@ DEFINE_TRACE(MatchedProperties)
     visitor->trace(properties);
 }
 
+// TODO(thakis): Remove this once http://crbug.com/488634 is fixed.
+MatchResult::MatchResult() = default;
+
 void MatchResult::addMatchedProperties(const StylePropertySet* properties, unsigned linkMatchType, PropertyWhitelistType propertyWhitelistType)
 {
     m_matchedProperties.grow(m_matchedProperties.size() + 1);