toolchain: add new debugging tool using magenta_debug

toolchain/mxdbg/client/line-ed/hook.c

@@ -0,0 +1,41 @@
+#include "hook.h"
+
+#include "line-ed.h"
+
+void line_ed_add_hook(struct line_ed *ed, struct line_ed_hook *hook)
+{
+	fx_queue_push_back(&ed->l_hooks, &hook->hook_entry);
+}
+
+void line_ed_remove_hook(struct line_ed *ed, struct line_ed_hook *hook)
+{
+	fx_queue_delete(&ed->l_hooks, &hook->hook_entry);
+}
+
+void hook_keypress(struct line_ed *ed, fx_keycode key)
+{
+	fx_queue_entry *entry = fx_queue_first(&ed->l_hooks);
+	while (entry) {
+		struct line_ed_hook *hook
+			= fx_unbox(struct line_ed_hook, entry, hook_entry);
+		if (hook->hook_keypress) {
+			hook->hook_keypress(ed, hook, key);
+		}
+
+		entry = fx_queue_next(entry);
+	}
+}
+
+void hook_buffer_modified(struct line_ed *ed)
+{
+	fx_queue_entry *entry = fx_queue_first(&ed->l_hooks);
+	while (entry) {
+		struct line_ed_hook *hook
+			= fx_unbox(struct line_ed_hook, entry, hook_entry);
+		if (hook->hook_buffer_modified) {
+			hook->hook_buffer_modified(ed, hook);
+		}
+
+		entry = fx_queue_next(entry);
+	}
+}