GN: Move towards only using / on Windows

tools/gn/path_output.h

Index: tools/gn/path_output.h
diff --git a/tools/gn/path_output.h b/tools/gn/path_output.h
index 33227d48641c6a9daf54ee0da12f691f249cbec1..00ce33b46d5ddb155d6ab4b1eaa7f10ffac9a473 100644
--- a/tools/gn/path_output.h
+++ b/tools/gn/path_output.h
@@ -34,8 +34,7 @@ class PathOutput {
   };
 
   PathOutput(const SourceDir& current_dir,
-             EscapingMode escaping,
-             bool convert_slashes);
+             EscapingMode escaping);
   ~PathOutput();
 
   // Read-only since inverse_current_dir_ is computed depending on this.
@@ -43,12 +42,6 @@ class PathOutput {
 
   const SourceDir& current_dir() const { return current_dir_; }
 
-  // When true, converts slashes to the system-type path separators (on
-  // Windows, this is a backslash, this is a NOP otherwise).
-  //
-  // Read-only since inverse_current_dir_ is computed depending on this.
-  bool convert_slashes_to_system() const { return options_.convert_slashes; }
-
   // When the output escaping is ESCAPE_SHELL, the escaper will normally put
   // quotes around suspect things. If this value is set to true, we'll disable
   // the quoting feature. This means that in ESCAPE_SHELL mode, strings with