Add WTF::String::emptyString16Bit

Source/wtf/text/StringStatics.cpp

Index: Source/wtf/text/StringStatics.cpp
diff --git a/Source/wtf/text/StringStatics.cpp b/Source/wtf/text/StringStatics.cpp
index 099f00115619cdf3403f25e96563bff563f4b6f2..a20f3c05d1b8e679426ad48da6e7bedf9e473086 100644
--- a/Source/wtf/text/StringStatics.cpp
+++ b/Source/wtf/text/StringStatics.cpp
@@ -34,11 +34,13 @@
 
 namespace WTF {
 
-StringImpl* StringImpl::empty()
+StringImpl* StringImpl::empty(bool is8Bit)
 {
-    DEFINE_STATIC_LOCAL(StringImpl, emptyString, (ConstructEmptyString));
-    WTF_ANNOTATE_BENIGN_RACE(&emptyString, "Benign race on StringImpl::emptyString reference counter");
-    return &emptyString;
+    DEFINE_STATIC_LOCAL(StringImpl, empty8BitString, (ConstructEmpty8BitString));
+    DEFINE_STATIC_LOCAL(StringImpl, empty16BitString, (ConstructEmpty16BitString));
+    WTF_ANNOTATE_BENIGN_RACE(&empty8BitString, "Benign race on StringImpl::empty8BitString reference counter");
+    WTF_ANNOTATE_BENIGN_RACE(&empty16BitString, "Benign race on StringImpl::empty16BitString reference counter");
+    return is8Bit ? &empty8BitString : &empty16BitString;
 }
 
 WTF_EXPORT DEFINE_GLOBAL(AtomicString, nullAtom)