WIP (Introduce WTF::NonNullPtr<T>.)

Source/wtf/Forward.h

Index: Source/wtf/Forward.h
diff --git a/Source/wtf/Forward.h b/Source/wtf/Forward.h
index f1ab5e2f579400d6f2e0ed1da2fb22f92db32f0e..1f54600d3ad6e85b3862eb12424ded9bf39e5f8f 100644
--- a/Source/wtf/Forward.h
+++ b/Source/wtf/Forward.h
@@ -25,6 +25,7 @@
 
 namespace WTF {
     template<typename T> class Function;
+    template<typename T> class NonNullPtr;
     template<typename T> class OwnArrayPtr;
     template<typename T> class OwnPtr;
     template<typename T> class PassOwnArrayPtr;
@@ -53,6 +54,7 @@ namespace WTF {
 }
 
 using WTF::Function;
+using WTF::NonNullPtr;
 using WTF::OwnArrayPtr;
 using WTF::OwnPtr;
 using WTF::PassOwnArrayPtr;