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/SymbolFile/DWARF/SymbolFileDWARF.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
index d82b3d4..3927745 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -3918,7 +3918,7 @@
                                             NULL);
             GetObjectFile()->GetModule()->ReportError(
                 "0x%8.8x: %s has an invalid location: %s", die.GetOffset(),
-                die.GetTagAsCString(), strm.GetString().c_str());
+                die.GetTagAsCString(), strm.GetData());
           }
         }
         SymbolFileDWARFDebugMap *debug_map_symfile = GetDebugMapSymfile();