I think this happens when a driver is disposed why search is in
progress. So, we need to make defensive copies.
This also makes me realize that we don't handle situations when
a driver instance is disposed, but it has pending requests, such as
getResult(), getIndex(), etc - actually any getXXX(), and search. As
it is now, I think we just leave these Future(s) and they never
complete.
R=brianwilkerson@google.com
BUG=
Review-Url: https://codereview.chromium.org/2818163003 .
Konstantin Shcheglov
124f874b4a