Oilpan: Allowing hashing of RawPtr.

Source/wtf/RawPtr.h

Index: Source/wtf/RawPtr.h
diff --git a/Source/wtf/RawPtr.h b/Source/wtf/RawPtr.h
index ac60e44768a2a950cfd6d5564e5d5b79ba54c26d..146aaf3d5c639a2e402a4cad2ba0d6ada072cf80 100644
--- a/Source/wtf/RawPtr.h
+++ b/Source/wtf/RawPtr.h
@@ -32,6 +32,7 @@
 #define WTF_RawPtr_h
 
 #include <algorithm>
+#include "wtf/HashTableDeletedValueType.h"
 
 // Ptr is a simple wrapper for a raw pointer that provides the
 // interface (get, clear) of other pointer types such as RefPtr,
@@ -61,6 +62,10 @@ public:
     {
     }
 
+    // Hash table deleted values, which are only constructed and never copied or destroyed.
+    RawPtr(HashTableDeletedValueType) : m_ptr(hashTableDeletedValue()) { }
+    bool isHashTableDeletedValue() const { return m_ptr == hashTableDeletedValue(); }
+
     T* get() const { return m_ptr; }
     void clear() { m_ptr = 0; }
     // FIXME: oilpan: Remove release and leakRef once we remove RefPtrWillBeRawPtr.
@@ -107,6 +112,7 @@ public:
         std::swap(m_ptr, o.m_ptr);
     }
 
+    static T* hashTableDeletedValue() { return reinterpret_cast<T*>(-1); }
 
 private:
     T* m_ptr;