Refactor GetNextPersistentVariableName into a non-virtual method
that takes a prefix string. This simplifies the implementation and
allows plugins such as the Swift plugin to supply different prefixes
for return and error variables.

rdar://problem/39299889

Differential Revision: https://reviews.llvm.org/D46088

llvm-svn: 331235
diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp
index 0062bb8..4da5492 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp
@@ -665,7 +665,9 @@
 }
 
 ConstString ClangUserExpression::ResultDelegate::GetName() {
-  return m_persistent_state->GetNextPersistentVariableName(*m_target_sp);
+  auto prefix = m_persistent_state->GetPersistentVariablePrefix();
+  return m_persistent_state->GetNextPersistentVariableName(*m_target_sp,
+                                                           prefix);
 }
 
 void ClangUserExpression::ResultDelegate::DidDematerialize(