Use Muhenkan as a hot-key. See crosbug.com/2543 (comment #25) for details.

src/xkbutil.c

 #include <string.h>
 #include <glib.h>
 #include "xkbutil.h"
 
 #ifndef XKB_RULES_XML_FILE
 #define XKB_RULES_XML_FILE "/usr/share/X11/xkb/rules/evdev.xml"
 #endif
 
 static IBusEngineDesc *
 ibus_xkb_engine_new (gchar    *layout,
@@ skipping 10 matching lines @@
 
     engine_name = g_strdup_printf ("xkb:%s:%s:%s", layout, variant, language);
     if (variant_desc && *variant_desc) {
         engine_longname = g_strdup_printf ("%s - %s", layout_desc, variant_desc);
     }
 
     if (variant && *variant) {
         engine_layout = g_strdup_printf ("%s(%s)", layout, variant);
     }
 
-    /* Adds special hotkey on Japanese keyboard to activate English input
-     * TODO(suzhe): make sure the corresponding key on ChromeOS device generates
-     * the same key symbol.*/
+    /* Adds special hotkey on Japanese keyboard to activate English input. */
     if (g_strcmp0(language, "jpn") == 0) {
-        engine_hotkeys = "Eisu_toggle";
+        engine_hotkeys = "Muhenkan";
     }
 
     engine = ibus_engine_desc_new2(engine_name,
                                    engine_longname ? engine_longname : layout_desc,
                                    "",
                                    language,
                                    "",
                                    "",
                                    "",
                                    engine_layout ? engine_layout : layout,
@@ skipping 181 matching lines @@
 
     engines = ibus_xkb_list_engines ();
 
     for (p = engines; p != NULL; p = p->next) {
         ibus_component_add_engine (component, (IBusEngineDesc *) p->data);
     }
 
     g_list_free (engines);
     return component;
 }