KeyEvent work.

Gets KeyEvents to work with the new Desktop classes.

A few things were required:
- Pass a real HWND to InputMethodWin, since it can't rely on Widget::GetNativeView() (NativeView = aura::Window*).
- Construct a InputMethodWin in DesktopRootWindowHostWin, and wire up relevant IME messages to it.
- Forward key events from DRWHW into the RootWindow, make sure DesktopNativeWidgetAura forwards them to the Widget.

http://crbug.com/146077
R=sky@chromium.org,scottmg@chromium.org,erg@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=156901

[Ben Goodger (Google), 2012-09-14 20:25:55]

sky: review
jam/scottmg/erg: fyi as an example of how a fairly complex  NOTIMPLEMENTED can
be resolved on the windows side.

[sky, 2012-09-14 22:14:46]

LGTM