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/Commands/CommandObjectThread.cpp b/lldb/source/Commands/CommandObjectThread.cpp
index ccab6ea..9771894 100644
--- a/lldb/source/Commands/CommandObjectThread.cpp
+++ b/lldb/source/Commands/CommandObjectThread.cpp
@@ -675,8 +675,8 @@
       if (synchronous_execution) {
         // If any state changed events had anything to say, add that to the
         // result
-        if (stream.GetData())
-          result.AppendMessage(stream.GetData());
+        if (stream.GetSize() > 0)
+          result.AppendMessage(stream.GetString());
 
         process->GetThreadList().SetSelectedThreadByID(thread->GetID());
         result.SetDidChangeProcessState(true);
@@ -853,8 +853,8 @@
         if (synchronous_execution) {
           // If any state changed events had anything to say, add that to the
           // result
-          if (stream.GetData())
-            result.AppendMessage(stream.GetData());
+          if (stream.GetSize() > 0)
+            result.AppendMessage(stream.GetString());
 
           result.SetDidChangeProcessState(true);
           result.SetStatus(eReturnStatusSuccessFinishNoResult);
@@ -1183,8 +1183,8 @@
         if (synchronous_execution) {
           // If any state changed events had anything to say, add that to the
           // result
-          if (stream.GetData())
-            result.AppendMessage(stream.GetData());
+          if (stream.GetSize() > 0)
+            result.AppendMessage(stream.GetString());
 
           result.SetDidChangeProcessState(true);
           result.SetStatus(eReturnStatusSuccessFinishNoResult);