Make calls to AtomicString(const String&) explicit in svg/

Source/core/css/resolver/StyleBuilderConverter.cpp

Index: Source/core/css/resolver/StyleBuilderConverter.cpp
diff --git a/Source/core/css/resolver/StyleBuilderConverter.cpp b/Source/core/css/resolver/StyleBuilderConverter.cpp
index 3024c9654392dba5783b8fcde007f7d5901d6e63..c66894a17ebf3d763f407090e381b0d996f53abc 100644
--- a/Source/core/css/resolver/StyleBuilderConverter.cpp
+++ b/Source/core/css/resolver/StyleBuilderConverter.cpp
@@ -34,12 +34,12 @@
 
 namespace WebCore {
 
-String StyleBuilderConverter::convertFragmentIdentifier(StyleResolverState& state, CSSValue* value)
+AtomicString StyleBuilderConverter::convertFragmentIdentifier(StyleResolverState& state, CSSValue* value)
 {
     CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(value);
     if (primitiveValue->isURI())
         return SVGURIReference::fragmentIdentifierFromIRIString(primitiveValue->getStringValue(), state.document());
-    return String();
+    return nullAtom;
 }
 
 Length StyleBuilderConverter::convertLength(StyleResolverState& state, CSSValue* value)