Replace boost::intrusive_ptr with TfIntrusiveTrackingPtr in `Usd_…

…Shared`

pxr/usd/usd/shared.h

@@ -27,8 +27,8 @@
 #include "pxr/pxr.h"
 #include "pxr/usd/usd/api.h"
 #include "pxr/base/tf/hash.h"
+#include "pxr/base/tf/trackingPtr.h"
 
-#include <boost/smart_ptr/intrusive_ptr.hpp>
 #include <atomic>
 
 PXR_NAMESPACE_OPEN_SCOPE
@@ -66,11 +66,13 @@ template <class T>
 struct Usd_Shared
 {
     // Construct a Usd_Shared with a value-initialized T instance.
-    Usd_Shared() : _held(new Usd_Counted<T>()) {}
+    Usd_Shared() : _held(TfIntrusiveMakeTrackingPtr<Usd_Counted<T>>()) {}
     // Create a copy of \p obj.
-    explicit Usd_Shared(T const &obj) : _held(new Usd_Counted<T>(obj)) {}
+    explicit Usd_Shared(T const &obj) :
+        _held(TfIntrusiveMakeTrackingPtr<Usd_Counted<T>>(obj)) {}
     // Move from \p obj.
-    explicit Usd_Shared(T &&obj) : _held(new Usd_Counted<T>(std::move(obj))) {}
+    explicit Usd_Shared(T &&obj) :
+        _held(TfIntrusiveMakeTrackingPtr<Usd_Counted<T>>(std::move(obj))) {}
 
     // Create an empty shared, which may not be accessed via Get(),
     // GetMutable(), IsUnique(), Clone(), or MakeUnique().  This is useful when
@@ -86,7 +88,7 @@ struct Usd_Shared
     // Return true if no other Usd_Shared instance shares this instance's data.
     bool IsUnique() const { return _held->count == 1; }
     // Make a new copy of the held data and refer to it.
-    void Clone() { _held.reset(new Usd_Counted<T>(Get())); }
+    void Clone() { _held = TfIntrusiveMakeTrackingPtr<Usd_Counted<T>>(Get()); }
     // Ensure this Usd_Shared instance has unique data.  Equivalent to:
     // \code
     // if (not shared.IsUnique()) { shared.Clone(); }
@@ -108,7 +110,7 @@ struct Usd_Shared
         return TfHash()(sh._held->data);
     }
 private:
-    boost::intrusive_ptr<Usd_Counted<T>> _held;
+    TfIntrusiveTrackingPtr<Usd_Counted<T>> _held;
 };