Warn on executing command on unsupported elements.

Warn on executing command on unsupported elements.

Elements which don't have corresponding entries can be focused. (for example, when buttons are focused by <Tab>.)
When they are focused, canExecute of commands are called and warnings are emitted in CommandUtil.getCommandEntry().
This CL warn more specific (really suspicious) case. That is, a command executed on an element which doesn't have corresponding entry.

BUG=411790
TEST=manually tested

Committed: https://crrev.com/712add9076ac2552ff32ce9be6d78289989ca7af
Cr-Commit-Position: refs/heads/master@{#294125}

[fukino, 2014-09-09 01:22:30]

fukino@chromium.org changed reviewers:
+ yoshiki@chromium.org

[fukino, 2014-09-09 01:23:00]

@yoshiki - Could you take a look? Thanks!

[yoshiki, 2014-09-10 05:22:23]

lgtm

[fukino, 2014-09-10 05:35:24]

The CQ bit was checked by fukino@chromium.org

[commit-bot: I haz the power, 2014-09-10 05:36:41]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/fukino@chromium.org/550943003/1

[commit-bot: I haz the power, 2014-09-10 06:35:44]

Committed patchset #1 (id:1) as 283c0174942cf11dbb29ff2ab5c76db9a1e35e82

[commit-bot: I haz the power, 2014-09-10 06:41:00]

Patchset 1 (id:??) landed as
https://crrev.com/712add9076ac2552ff32ce9be6d78289989ca7af
Cr-Commit-Position: refs/heads/master@{#294125}