Revert of 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 58d069a232391207eea01d3e3c2b8fb59bbff3c6..2d337d6c53ec6f34b29eac2718920a4a2d3bcb29 100644
--- a/third_party/WebKit/Source/wtf/text/WTFString.cpp
+++ b/third_party/WebKit/Source/wtf/text/WTFString.cpp
@@ -70,16 +70,6 @@
     : m_impl(characters ? StringImpl::create(
                               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())