Small cleanup: move all library private key code to Library class

runtime/vm/scanner.h

Index: runtime/vm/scanner.h
===================================================================
--- runtime/vm/scanner.h	(revision 32509)
+++ runtime/vm/scanner.h	(working copy)
@@ -44,12 +44,6 @@
   // Dummy token index reflecting an unknown source position.
   static const intptr_t kNoSourcePos = 0;
 
-  // Character used to indicate a private identifier.
-  static const char kPrivateIdentifierStart  = '_';
-
-  // Character used to separate the private identifier from the key.
-  static const char kPrivateKeySeparator = '@';
-
   typedef ZoneGrowableArray<TokenDescriptor> GrowableTokenStream;
 
   // Initializes scanner to scan string source.
@@ -80,9 +74,6 @@
 
   static void InitOnce();
 
-  // Allocated a private key which is used for name mangling.
-  static RawString* AllocatePrivateKey(const Library& library);
-
   // Return true if str is an identifier.
   static bool IsIdent(const String& str);