Redo escaping in GN

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 = 1,
+  ESCAPE_NINJA,
 
-  // Shell string escaping.
-  ESCAPE_SHELL = 2,
+  // For writing commands to ninja files.
+  ESCAPE_NINJA_COMMAND,
+};
 
-  // For writing shell commands to ninja files.
-  ESCAPE_NINJA_SHELL = ESCAPE_NINJA | ESCAPE_SHELL,
+enum EscapingPlatform {
+  // Do escaping for the current platform.
+  ESCAPE_PLATFORM_CURRENT,
 
-  ESCAPE_JSON = 4,
+  // Force escaping for the given platform.
+  ESCAPE_PLATFORM_POSIX,
+  ESCAPE_PLATFORM_WIN,
 };
 
 struct EscapeOptions {
   EscapeOptions()
       : mode(ESCAPE_NONE),
-        convert_slashes(false),
+        platform(ESCAPE_PLATFORM_CURRENT),
         inhibit_quoting(false) {
   }
 
   EscapingMode mode;
 
-  // When set, converts forward-slashes to system-specific path separators.
-  bool convert_slashes;
+  // Controls how "fork" escaping is done. You will generally want to keep the
+  // default "current" platform.
+  EscapingPlatform platform;
 
   // When the escaping mode is ESCAPE_SHELL, the escaper will normally put
   // quotes around things with spaces. If this value is set to true, we'll
   // disable the quoting feature and just add the spaces.
   //
   // This mode is for when quoting is done at some higher-level. Defaults to
-  // false.
+  // false. Note that Windows has strange behavior where the meaning of the
+  // backslashes changes according to if it is followed by a quote. The
+  // escaping rules assume that a double-quote will be appended to the result.
   bool inhibit_quoting;
 };
 
 // Escapes the given input, returnining the result.
 //
 // If needed_quoting is non-null, whether the string was or should have been
 // (if inhibit_quoting was set) quoted will be written to it. This value should
 // be initialized to false by the caller and will be written to only if it's
 // true (the common use-case is for chaining calls).
 std::string EscapeString(const base::StringPiece& str,
                          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_