Support more configurability in GN toolchains

tools/gn/escape.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef TOOLS_GN_ESCAPE_H_
 #define TOOLS_GN_ESCAPE_H_
 
 #include <iosfwd>
 
 #include "base/strings/string_piece.h"
 
 enum EscapingMode {
   // No escaping.
   ESCAPE_NONE,
 
   // Ninja string escaping.
   ESCAPE_NINJA,
 
-  // For writing commands to ninja files.
+  // For writing commands to ninja files. This assumes the output is "one
+  // thing" like a filename, so will escape or quote spaces as necessary for
+  // both Ninja and the shell to keep that thing together.
   ESCAPE_NINJA_COMMAND,
+
+  // For writing preformatted shell commands to Ninja files. This assumes the
+  // output already has the proper quoting and may include special shell
+  // shell characters which we want to pass to the shell (like when writing
+  // tool commands). Only Ninja "$" are escaped.
+  ESCAPE_NINJA_PREFORMATTED_COMMAND,
 };
 
 enum EscapingPlatform {
   // Do escaping for the current platform.
   ESCAPE_PLATFORM_CURRENT,
 
   // Force escaping for the given platform.
   ESCAPE_PLATFORM_POSIX,
   ESCAPE_PLATFORM_WIN,
 };
@@ skipping 32 matching lines @@
                          const EscapeOptions& options,
                          bool* needed_quoting);
 
 // Same as EscapeString but writes the results to the given stream, saving a
 // copy.
 void EscapeStringToStream(std::ostream& out,
                           const base::StringPiece& str,
                           const EscapeOptions& options);
 
 #endif  // TOOLS_GN_ESCAPE_H_