Add power-user keyboard mode for ChromeOS with Search key acting as a typical Fn key.

ash/accelerators/accelerator_table.cc

Index: ash/accelerators/accelerator_table.cc
diff --git a/ash/accelerators/accelerator_table.cc b/ash/accelerators/accelerator_table.cc
index 57ba21791c865c289c6fbf07a79c23c72bf48742..059e76c88530aa07e4b144bc64bcc8ce0fbaad2a 100644
--- a/ash/accelerators/accelerator_table.cc
+++ b/ash/accelerators/accelerator_table.cc
@@ -108,10 +108,12 @@ const AcceleratorData kAcceleratorData[] = {
     CYCLE_BACKWARD_LINEAR },
   { true, ui::VKEY_T, ui::EF_SHIFT_DOWN | ui::EF_CONTROL_DOWN, RESTORE_TAB },
   { true, ui::VKEY_PRINT, ui::EF_NONE, TAKE_SCREENSHOT },
-  // On Chrome OS, Search key is mapped to LWIN.
-  { true, ui::VKEY_LWIN, ui::EF_NONE, TOGGLE_APP_LIST },
+  // On Chrome OS, Search key is mapped to LWIN. Search key bindings should act
+  // on release instead of press, since the press can be eaten when using Search
+  // as a modifier key for extended keyboard shortcuts.
+  { false, ui::VKEY_LWIN, ui::EF_NONE, TOGGLE_APP_LIST },

[Yusuke Sato, 2012/11/26 06:09:38]

Could you keep the accelerator to be triggered on press? (e.g. by rewriting
ui::VKEY_LWIN to ui::VKEY_UNKNOWN or something when the new feature is enabled.)

I think release accelerators have been a source of anxiety for us and are
something we really want to avoid whenever possible. For example, please take a
look at comments near 'case NEXT_IME' in AcceleratorController::PerformAction().

Another issue for this change is latency. The use who is used to the current
Search behavior might feel laggy if we do this since the app menu is not shown
until the user releases Search.

[danakj, 2012/11/26 17:20:16]

If we keep it on press, then when the feature is enable, the Search key can't do
anything except be a modifier. This allows it to still pop up the Apps menu. I
think losing access to the apps menu would be a bad thing.. It functions similar
to other desktop OSes that provide a modifer key for running various things, but
also provide access to the apps menu when not used as a modifier.
Making this a bit laggy seems better than making it stop working altogether.

I thought at first we could drop the press, and then when the release happened,
generate a press and release together. But the system seems designed to edit
events, not to insert new ones. And turning the release into a press seems bad,
because then someone watching would see the Search key as being held down.

Do you have some idea of how to let us use Search as a modifer, and still use it
to access the apps menu, without binding it to release?

What if it was bound to release only when the feature was enabled?

[Yusuke Sato, 2012/11/26 21:15:05]

Oh now I understood what you wanted to do. Thanks for the explanation.

On 2012/11/26 17:20:16, danakj wrote:
Fair enough.
Sounds good. Please make sure to add some code to accelerator_controller.cc
which is similar to this:

    case DISABLE_CAPS_LOCK:
      if (previous_event_type == ui::ET_KEY_RELEASED)
        return false;

so TOGGLE_APP_LIST would not fire when you press Search+<something>, release
<something>, then release Search.

Please also check my comment in event_rewriter.cc in Patch Set 6.

   { true, ui::VKEY_MEDIA_LAUNCH_APP2, ui::EF_NONE, TOGGLE_APP_LIST },
-  { true, ui::VKEY_LWIN, ui::EF_ALT_DOWN, TOGGLE_CAPS_LOCK },
+  { false, ui::VKEY_LWIN, ui::EF_ALT_DOWN, TOGGLE_CAPS_LOCK },

[Yusuke Sato, 2012/11/26 06:09:38]

I guess TOGGLE_CAPS_LOCK is not fired if the user presses/releases keys in this
order: press Alt, press Search, release Alt, release Search.

I think the easiest way to avoid this kind of problem would be to avoid release
accelerators.

[danakj, 2012/11/26 17:20:16]

I can make it not rewrite the Search press when another modifier is being used.
I did that at first, but the apps menu didn't work like that, so I made it a
release modifier, and just made this match.

[danakj, 2012/11/26 19:36:26]

Done.

   { true, ui::VKEY_VOLUME_MUTE, ui::EF_NONE, VOLUME_MUTE },
   { true, ui::VKEY_VOLUME_DOWN, ui::EF_NONE, VOLUME_DOWN },
   { true, ui::VKEY_VOLUME_UP, ui::EF_NONE, VOLUME_UP },