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/LibCxxOptional.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxxOptional.cpp
index 7ae251b..1160215 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxxOptional.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibCxxOptional.cpp
@@ -20,7 +20,7 @@
     Update();
   }
 
-  size_t GetIndexOfChildWithName(const ConstString &name) override {
+  size_t GetIndexOfChildWithName(ConstString name) override {
     return formatters::ExtractIndexFromString(name.GetCString());
   }