Redo GN "args" command

tools/gn/value.cc

Index: tools/gn/value.cc
diff --git a/tools/gn/value.cc b/tools/gn/value.cc
index 1fb7155dc1b609d410f884d5f3163b7b016ca760..3632ddf4a80c5b1cfaab255c00b2467ca92d2cd5 100644
--- a/tools/gn/value.cc
+++ b/tools/gn/value.cc
@@ -5,6 +5,7 @@
 #include "tools/gn/value.h"
 
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
 #include "tools/gn/scope.h"
 
 Value::Value()
@@ -130,8 +131,17 @@ std::string Value::ToString(bool quote_string) const {
     case INTEGER:
       return base::Int64ToString(int_value_);
     case STRING:
-      if (quote_string)
-        return "\"" + string_value_ + "\"";
+      if (quote_string) {
+        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: {
       std::string result = "[";