Change DataPersistent constructor to allow one line initialisation.

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

Index: third_party/WebKit/Source/core/style/DataPersistent.h
diff --git a/third_party/WebKit/Source/core/style/DataPersistent.h b/third_party/WebKit/Source/core/style/DataPersistent.h
index 3672b6a7909f96fbd37a49502e3ef5634a75188b..ba18789be6a04f8e81c69e41885bbf242d622922 100644
--- a/third_party/WebKit/Source/core/style/DataPersistent.h
+++ b/third_party/WebKit/Source/core/style/DataPersistent.h
@@ -29,7 +29,11 @@ class DataPersistent {
   USING_FAST_MALLOC(DataPersistent);
 
  public:
-  DataPersistent() : own_copy_(false) {}
+  DataPersistent()
+      : data_(WTF::WrapUnique(new Persistent<T>(T::Create()))),
+        own_copy_(true) {}
+
+  DataPersistent(std::nullptr_t) : data_(nullptr), own_copy_(false) {}
 
   DataPersistent(const DataPersistent& other) : own_copy_(false) {
     if (other.data_)