Pass ConstString by value (NFC)

My apologies for the large patch. With the exception of ConstString.h
itself it was entirely produced by sed.

ConstString has exactly one const char * data member, so passing a
ConstString by reference is not any more efficient than copying it by
value. In both cases a single pointer is passed. But passing it by
value makes it harder to accidentally return the address of a local
object.

(This fixes rdar://problem/48640859 for the Apple folks)

Differential Revision: https://reviews.llvm.org/D59030

llvm-svn: 355553
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
index 15d3491..e63452e 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
@@ -299,7 +299,7 @@
 }
 
 size_t lldb_private::formatters::LibCxxMapIteratorSyntheticFrontEnd::
-    GetIndexOfChildWithName(const ConstString &name) {
+    GetIndexOfChildWithName(ConstString name) {
   if (name == ConstString("first"))
     return 0;
   if (name == ConstString("second"))
@@ -429,7 +429,7 @@
 }
 
 size_t lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEnd::
-    GetIndexOfChildWithName(const ConstString &name) {
+    GetIndexOfChildWithName(ConstString name) {
   if (name == ConstString("__ptr_"))
     return 0;
   if (name == ConstString("count"))