Ignore EnterNotify and ExitNotify events from NativeViewGlSurfaceGLX's window.

Ignore EnterNotify and LeaveNotify events from NativeViewGlSurfaceGLX's window.
https://codereview.chromium.org/296003010 added a child window to the toplevel
X window. As a result of the CL, an EnterNotify event is sent immediately
after each mouse press. WindowTreeHostX11:Dispatch() transforms the EnterNotify
to a synthetic mouse move.

In terms of HTML events, the CL causes an 'onmousemove' event to be fired
immediately after the 'onmousedown' event. This differs from the previous
behavior where the initial 'onmousemove' event was always fired some
indeterminate time after the 'onmousedown'.

For the sake of safety, this CL suppresses the extra EnterNotify.

BUG=385716
TEST=None

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=278485

[pkotwicz, 2014-06-18 22:46:23]

Sadrul, PTAL

Extra info:
https://x20web.corp.google.com/~pkotwicz/drag_delay/index.html is a web page
which demonstrates the change in the delay.

The undesired EnterNotify is sent with mode == NotifyGrab both on CrOS and
desktop

Based on some discussion with kevers@ it seems really unlikely that any web page
relies on the old behavior. However, for the sake of properness we should change
the
behavior after we have determined that it is ok to do so.

[piman, 2014-06-18 22:51:02]

LGTM fwiw

[sadrul, 2014-06-19 13:20:54]

lgtm

[pkotwicz, 2014-06-19 13:37:03]

The CQ bit was checked by pkotwicz@chromium.org

[commit-bot: I haz the power, 2014-06-19 13:38:36]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/346673002/80001

[pkotwicz, 2014-06-19 13:43:41]

The CQ bit was unchecked by pkotwicz@chromium.org

[pkotwicz, 2014-06-19 13:44:24]

The CQ bit was checked by pkotwicz@chromium.org

[commit-bot: I haz the power, 2014-06-19 13:45:30]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/346673002/80001

[commit-bot: I haz the power, 2014-06-19 21:13:35]

Change committed as 278485