In Windows the right-hand Alt key serves as AltGraph (ISO-Level-3-Shift) on some layouts (for example, many European language layouts), to allow generating additional printable characters. Internally the key generates Ctrl+Alt modifiers, so that Chrome reports all of Control, Alt and AltGraph in the flags for these keys. In this change, Chrome distinguishes AltGraph from Ctrl+Alt under Windows for consistency with modifiers on other platforms. See the comments for how this helps developers.