gn: beginnings of format command

tools/gn/location.h

Index: tools/gn/location.h
diff --git a/tools/gn/location.h b/tools/gn/location.h
index aad3960deb002e9d425d11948c2fdb3c7c15a66d..fc6288e52d0d2bb77bb7f3ebc33c25f7894f5135 100644
--- a/tools/gn/location.h
+++ b/tools/gn/location.h
@@ -13,11 +13,12 @@ class InputFile;
 class Location {
  public:
   Location();
-  Location(const InputFile* file, int line_number, int char_offset);
+  Location(const InputFile* file, int line_number, int char_offset, int byte);
 
   const InputFile* file() const { return file_; }
   int line_number() const { return line_number_; }
   int char_offset() const { return char_offset_; }
+  int byte() const { return byte_; }
 
   bool operator==(const Location& other) const;
   bool operator!=(const Location& other) const;
@@ -32,6 +33,7 @@ class Location {
   const InputFile* file_;  // Null when unset.
   int line_number_;  // -1 when unset.
   int char_offset_;  // -1 when unset.
+  int byte_;
 };
 
 // Represents a range in a source file. Used for error reporting.