Do not crash webview if its group creation fails due to a dead process

Failure by webview to create a process group for newly spawned child is
treated as a fatal error. This is done to avoid leaving children in
the parent's process group because such relationship can lead to
side-effects, like freezing the parent when the child's group is being
frozen.
However, if the child died before it could be added into a process
group, there is no such danger, therefore such failure does not have
to crash the parent process.
Check for this situation and when createProcessGroup() fails because
the child is dead, just log the error and keep going.

Bug: 270103958
Change-Id: I129da0838fc14ac0dbda43de49bcf47918f1822d
Signed-off-by: Suren Baghdasaryan <surenb@google.com>