Adding cython v0.20.2 in third-party.

third_party/cython/src/Cython/Compiler/Visitor.pxd

Index: third_party/cython/src/Cython/Compiler/Visitor.pxd
diff --git a/third_party/cython/src/Cython/Compiler/Visitor.pxd b/third_party/cython/src/Cython/Compiler/Visitor.pxd
new file mode 100644
index 0000000000000000000000000000000000000000..795eb9c2c6a3871b8f101bdb3b8b741d4ccae7a1
--- /dev/null
+++ b/third_party/cython/src/Cython/Compiler/Visitor.pxd
@@ -0,0 +1,50 @@
+cimport cython
+
+cdef class TreeVisitor:
+    cdef public list access_path
+    cdef dict dispatch_table
+
+    cpdef visit(self, obj)
+    cdef _visit(self, obj)
+    cdef find_handler(self, obj)
+    cdef _visitchild(self, child, parent, attrname, idx)
+    cdef dict _visitchildren(self, parent, attrs)
+    cpdef visitchildren(self, parent, attrs=*)
+
+cdef class VisitorTransform(TreeVisitor):
+    cpdef visitchildren(self, parent, attrs=*)
+    cpdef recurse_to_children(self, node)
+
+cdef class CythonTransform(VisitorTransform):
+    cdef public context
+    cdef public current_directives
+
+cdef class ScopeTrackingTransform(CythonTransform):
+    cdef public scope_type
+    cdef public scope_node
+    cdef visit_scope(self, node, scope_type)
+
+cdef class EnvTransform(CythonTransform):
+    cdef public list env_stack
+
+cdef class MethodDispatcherTransform(EnvTransform):
+    @cython.final
+    cdef _visit_binop_node(self, node)
+    @cython.final
+    cdef _find_handler(self, match_name, bint has_kwargs)
+    @cython.final
+    cdef _delegate_to_assigned_value(self, node, function, arg_list, kwargs)
+    @cython.final
+    cdef _dispatch_to_handler(self, node, function, arg_list, kwargs)
+    @cython.final
+    cdef _dispatch_to_method_handler(self, attr_name, self_arg,
+                                     is_unbound_method, type_name,
+                                     node, function, arg_list, kwargs)
+
+cdef class RecursiveNodeReplacer(VisitorTransform):
+     cdef public orig_node
+     cdef public new_node
+
+cdef class NodeFinder(TreeVisitor):
+    cdef node
+    cdef public bint found