Out-of-line WTF::String's destructor.

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

Index: third_party/WebKit/Source/wtf/text/WTFString.cpp
diff --git a/third_party/WebKit/Source/wtf/text/WTFString.cpp b/third_party/WebKit/Source/wtf/text/WTFString.cpp
index 2d337d6c53ec6f34b29eac2718920a4a2d3bcb29..58d069a232391207eea01d3e3c2b8fb59bbff3c6 100644
--- a/third_party/WebKit/Source/wtf/text/WTFString.cpp
+++ b/third_party/WebKit/Source/wtf/text/WTFString.cpp
@@ -71,6 +71,16 @@ String::String(const char* characters)
                               reinterpret_cast<const LChar*>(characters))
                         : nullptr) {}
 
+String::String(const String&) = default;
+
+String& String::operator=(const String&) = default;
+
+String::String(String&&) = default;
+
+String& String::operator=(String&&) = default;
+
+String::~String() {}
+
 void String::append(const StringView& string) {
   if (string.isEmpty())
     return;