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/LibCxxUnorderedMap.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp
index f4abe93..b2c38c9 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp
@@ -39,7 +39,7 @@
 
   bool MightHaveChildren() override;
 
-  size_t GetIndexOfChildWithName(const ConstString &name) override;
+  size_t GetIndexOfChildWithName(ConstString name) override;
 
 private:
   CompilerType m_element_type;
@@ -209,7 +209,7 @@
 }
 
 size_t lldb_private::formatters::LibcxxStdUnorderedMapSyntheticFrontEnd::
-    GetIndexOfChildWithName(const ConstString &name) {
+    GetIndexOfChildWithName(ConstString name) {
   return ExtractIndexFromString(name.GetCString());
 }