If keysym is ASCII control or space keys, directly map to keycode.

ui/events/keycodes/keyboard_code_conversion_x.cc

Index: ui/events/keycodes/keyboard_code_conversion_x.cc
diff --git a/ui/events/keycodes/keyboard_code_conversion_x.cc b/ui/events/keycodes/keyboard_code_conversion_x.cc
index a4a810e23a43004eb09af168daa797968e6d8a23..4bee80c46fa53ee47dc95fd6ad0daa06d2e99a49 100644
--- a/ui/events/keycodes/keyboard_code_conversion_x.cc
+++ b/ui/events/keycodes/keyboard_code_conversion_x.cc
@@ -492,7 +492,8 @@ KeyboardCode KeyboardCodeFromXKeyEvent(const XEvent* xev) {
   XLookupString(xkey, NULL, 0, &keysym, NULL);
   if (IsKeypadKey(keysym) || IsPrivateKeypadKey(keysym) ||
       IsCursorKey(keysym) || IsPFKey(keysym) || IsFunctionKey(keysym) ||
-      IsModifierKey(keysym)) {
+      IsModifierKey(keysym) || keysym == XK_Return || keysym == XK_Tab ||
+      keysym == XK_BackSpace || keysym == XK_space) {

[Yuki, 2014/10/23 06:33:44]

Do we want to support other control characters here?
For example, vertical tab, form feed, escape, etc.

We may want to treat all control characters in ASCII (0x01 to 0x1F) + space
(0x20) here.  You may want to add such a helper function, say
IsAsciiControlKey(keysym).  Though, note that space is not a control character.

[Shu Chen, 2014/10/23 07:00:17]

Done. Thanks for the suggestion.

     return KeyboardCodeFromXKeysym(keysym);
   }