Call TSF's SetFocus iff the current focused document manager is expected ones

This patch set introduces a new utility method named "IsFocused" and calls TSF's SetFocus if and only if the current focused document manager is expected ones.

Background:
Despite that TsfBridge is responsible for managing IME on/off state only for content area, TsfBridge::EnableIME and TsfBridge::DisableIME will be called even when other UI components such as OmniBox have input focus. In this case, we should not call TSF's SetFocus because it makes TSF confused.

BUG=141606
TEST=Manually tested on Windows 8 RTM with Metro mode.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=156343

[Seigo Nonaka, 2012-09-12 13:43:48]

lgtm

[Yohei Yukawa, 2012-09-12 13:45:47]

Adding sky@ as an owner of ui/.

Thanks!

[sky, 2012-09-12 14:45:24]

LGTM

[commit-bot: I haz the power, 2012-09-12 15:39:09]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/Yukawa@chromium.org/10933042/1003

[commit-bot: I haz the power, 2012-09-12 18:54:11]

Change committed as 156343