We should not be declaring forward declarations for nsString classes directly,
instead we should use nsStringFwd.h. This will make changing the underlying
types easier.
Before posting native key message from PluginInstanceChild, we need to check if the key combination could be a shortcut key, i.e., we need to check if Ctrl or Alt key is pressed. ModifierKeyState is a good class for checking it but it should be defined in an independent header file.
This patch separates the definition of ModifierKeyState to mozilla/widget/WinModifierKeyState.h and implement MaybeMatchShortcutKey() for PluginInstanceChild.
MozReview-Commit-ID: ZjLnJx02Ou
