Allow \n in GN string literals

tools/gn/parser.cc

Index: tools/gn/parser.cc
diff --git a/tools/gn/parser.cc b/tools/gn/parser.cc
index 79966b8ac59c4ce096b7124899df6d01046d4343..d3e2f0ff2efec7fa9cb33efac51f31d856239f4c 100644
--- a/tools/gn/parser.cc
+++ b/tools/gn/parser.cc
@@ -62,7 +62,8 @@ const char kGrammar_Help[] =
     "      escape           = `\\` ( \"$\" | `\"` | char ) .\n"
     "      BracketExpansion = \"{\" ( identifier | ArrayAccess | ScopeAccess "
                               ") \"}\" .\n"
-    "      expansion        = \"$\" ( identifier | BracketExpansion ) .\n"
+    "      Hex              = \"0x\" [0-9A-Fa-f][0-9A-Fa-f]\n"
+    "      expansion        = \"$\" ( identifier | BracketExpansion | Hex ) .\n"
     "      char             = /* any character except \"$\", `\"`, or newline "
                              "*/ .\n"
     "\n"
@@ -74,6 +75,9 @@ const char kGrammar_Help[] =
     "\n"
     "  All other backslashes represent themselves.\n"
     "\n"
+    "  To insert an arbitrary byte value, use $0xFF. For example, to\n"
+    "  insert a newline character: \"Line one$0x0ALine two\".\n"
+    "\n"
     "Punctuation\n"
     "\n"
     "  The following character sequences represent punctuation:\n"