Convert //tools to use std::unique_ptr

tools/gn/command_format.cc

Index: tools/gn/command_format.cc
diff --git a/tools/gn/command_format.cc b/tools/gn/command_format.cc
index ae36e37783e8792a0ced125f4b6b783ad8b3eab4..a054b21b9b9cef6aadd8877356036a1ef8da9e32 100644
--- a/tools/gn/command_format.cc
+++ b/tools/gn/command_format.cc
@@ -982,7 +982,7 @@ bool FormatStringToString(const std::string& input,
   }
 
   // Parse.
-  scoped_ptr<ParseNode> parse_node = Parser::Parse(tokens, &err);
+  std::unique_ptr<ParseNode> parse_node = Parser::Parse(tokens, &err);
   if (err.has_error()) {
     err.PrintToStdout();
     return false;