Replace WTF::emptyString{16Bit}() with a static global

third_party/WebKit/Source/wtf/text/StringBuilder.cpp

Index: third_party/WebKit/Source/wtf/text/StringBuilder.cpp
diff --git a/third_party/WebKit/Source/wtf/text/StringBuilder.cpp b/third_party/WebKit/Source/wtf/text/StringBuilder.cpp
index edf7c6a64c0fb28ae9596f0a0b7cff9e8647707e..3086eb99f330e5c68cf1e9a84a10f589d9aa4f47 100644
--- a/third_party/WebKit/Source/wtf/text/StringBuilder.cpp
+++ b/third_party/WebKit/Source/wtf/text/StringBuilder.cpp
@@ -35,7 +35,7 @@ namespace WTF {
 
 String StringBuilder::toString() {
   if (!m_length)
-    return emptyString();
+    return emptyString;
   if (m_string.isNull()) {
     if (m_is8Bit)
       m_string = String(characters8(), m_length);
@@ -61,7 +61,7 @@ AtomicString StringBuilder::toAtomicString() {
 
 String StringBuilder::substring(unsigned start, unsigned length) const {
   if (start >= m_length)
-    return emptyString();
+    return emptyString;
   if (!m_string.isNull())
     return m_string.substring(start, length);
   length = std::min(length, m_length - start);