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/LibStdcppUniquePointer.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibStdcppUniquePointer.cpp
index 335523e..451e58f 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibStdcppUniquePointer.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibStdcppUniquePointer.cpp
@@ -34,7 +34,7 @@
 
   bool MightHaveChildren() override;
 
-  size_t GetIndexOfChildWithName(const ConstString &name) override;
+  size_t GetIndexOfChildWithName(ConstString name) override;
 
   bool GetSummary(Stream &stream, const TypeSummaryOptions &options);
 
@@ -129,7 +129,7 @@
 }
 
 size_t LibStdcppUniquePtrSyntheticFrontEnd::GetIndexOfChildWithName(
-    const ConstString &name) {
+    ConstString name) {
   if (name == ConstString("ptr") || name == ConstString("pointer"))
     return 0;
   if (name == ConstString("del") || name == ConstString("deleter"))