gn/gyp: Escape \ in addition to $ and " in strings.

build/gyp_chromium

 #!/usr/bin/env python
 
 # Copyright (c) 2012 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.
 
 # This script is wrapper for Chromium that adds some support for how GYP
 # is invoked by Chromium beyond what can be done in the gclient hooks.
 
 import glob
@@ skipping 59 matching lines @@
   """Returns the given GYP key reformatted for GN.
 
   GYP dictionary keys can be almost anything, but in GN they are identifiers
   and must follow the same rules. This reformats such keys to be valid GN
   identifiers."""
   return ''.join([c if c in string.ascii_letters else '_' for c in key])
 
 
 def EscapeStringForGN(s):
   """Converts a string to a GN string literal."""
-  # Escape $ characters which have special meaning to GN.
-  return '"' + s.replace('$', '\\$').replace('"', '\\"') + '"'
+  for old, new in [('\\', '\\\\'), ('$', '\\$'), ('"', '\\"')]:
+    s = s.replace(old, new)
+  return '"' + s + '"'
 
 
 def ProcessGypDefinesItems(items):
   """Converts a list of strings to a list of key-value pairs."""
   result = []
   for item in items:
     tokens = item.split('=', 1)
     # Some GYP variables have hyphens, which we don't support.
     key = FormatKeyForGN(tokens[0])
     if len(tokens) == 2:
@@ skipping 335 matching lines @@
   args.extend(
       ['-I' + i for i in additional_include_files(supplemental_includes, args)])
 
   args.extend(['-D', 'gyp_output_dir=' + GetOutputDirectory()])
 
   print 'Updating projects from gyp files...'
   sys.stdout.flush()
 
   # Off we go...
   sys.exit(gyp.main(args))