Log and skip init of synthetic keyboard events for IE11

We don't have a solution synthetic keyboard events in IE11
so this patch changes it to skip the initialization and log
the issue instead of throwing an exception.

Bug: issue 8463
Change-Id: I8230e542c7a6ec74418d62f6c4b3aadf41de59e1
Review-Link: https://gwt-review.googlesource.com/#/c/10202/