Convert some Expression parser functions to StringRef.

llvm-svn: 286208
diff --git a/lldb/source/Symbol/ClangASTContext.cpp b/lldb/source/Symbol/ClangASTContext.cpp
index 75b7c3b..0c2cfe5 100644
--- a/lldb/source/Symbol/ClangASTContext.cpp
+++ b/lldb/source/Symbol/ClangASTContext.cpp
@@ -10050,14 +10050,14 @@
       m_persistent_variables(new ClangPersistentVariables) {}
 
 UserExpression *ClangASTContextForExpressions::GetUserExpression(
-    const char *expr, const char *expr_prefix, lldb::LanguageType language,
+    llvm::StringRef expr, llvm::StringRef prefix, lldb::LanguageType language,
     Expression::ResultType desired_type,
     const EvaluateExpressionOptions &options) {
   TargetSP target_sp = m_target_wp.lock();
   if (!target_sp)
     return nullptr;
 
-  return new ClangUserExpression(*target_sp.get(), expr, expr_prefix, language,
+  return new ClangUserExpression(*target_sp.get(), expr, prefix, language,
                                  desired_type, options);
 }