Don't allow direct access to StreamString's internal buffer.

This is a large API change that removes the two functions from
StreamString that return a std::string& and a const std::string&,
and instead provide one function which returns a StringRef.

Direct access to the underlying buffer violates the concept of
a "stream" which is intended to provide forward only access,
and makes porting to llvm::raw_ostream more difficult in the
future.

Differential Revision: https://reviews.llvm.org/D26698

llvm-svn: 287152
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibStdcppTuple.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibStdcppTuple.cpp
index d5fd386..c4a6e3d 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibStdcppTuple.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibStdcppTuple.cpp
@@ -73,7 +73,7 @@
         if (value_sp) {
           StreamString name;
           name.Printf("[%zd]", m_members.size());
-          value_sp->SetName(ConstString(name.GetData()));
+          value_sp->SetName(ConstString(name.GetString()));
 
           m_members.push_back(value_sp);
         }