Revert of tools/gn: fix escaping of backslashes

tools/gn/value.cc

Index: tools/gn/value.cc
diff --git a/tools/gn/value.cc b/tools/gn/value.cc
index 1a4215ce29e19569b344a5adf1507a603f8416b6..6dfe23417a4a4d6ee3183e613561bc7f434b1c18 100644
--- a/tools/gn/value.cc
+++ b/tools/gn/value.cc
@@ -124,27 +124,15 @@
       return base::Int64ToString(int_value_);
     case STRING:
       if (quote_string) {
-        std::string result = "\"";
-        bool hanging_backslash = false;
-        for (char ch : string_value_) {
-          // If the last character was a literal backslash and the next
-          // character could form a valid escape sequence, we need to insert
-          // an extra backslash to prevent that.
-          if (hanging_backslash && (ch == '$' || ch == '"' || ch == '\\'))
-            result += '\\';
-          // If the next character is a dollar sign or double quote, it needs
-          // to be escaped; otherwise it can be printed as is.
-          if (ch == '$' || ch == '"')
-            result += '\\';
-          result += ch;
-          hanging_backslash = (ch == '\\');
-        }
-        // Again, we need to prevent the closing double quotes from becoming
-        // an escape sequence.
-        if (hanging_backslash)
-          result += '\\';
-        result += '"';
-        return result;
+        std::string escaped = string_value_;
+        // First escape all special uses of a backslash.
+        ReplaceSubstringsAfterOffset(&escaped, 0, "\\$", "\\\\$");
+        ReplaceSubstringsAfterOffset(&escaped, 0, "\\\"", "\\\\\"");
+
+        // Now escape special chars.
+        ReplaceSubstringsAfterOffset(&escaped, 0, "$", "\\$");
+        ReplaceSubstringsAfterOffset(&escaped, 0, "\"", "\\\"");
+        return "\"" + escaped + "\"";
       }
       return string_value_;
     case LIST: {