Do not leak WK internal URL from pending item.

Extend WebStateTest.RestoreLargeSession test to verify that during
session restoration GetPendingItemIndex() returns -1 and
GetPendingItem() returns null.

Pending Item will appear after first post-restore navigation is
started, which happens before session restoration is considered
complete. Session restoration is complete after first post-restore
navigation is finished.

Bug: 877671
Change-Id: Iec922bc71a0101e14a7d12cca6c53a039d71674e
Reviewed-on: https://chromium-review.googlesource.com/c/1363958
Commit-Queue: Eugene But <eugenebut@chromium.org>
Reviewed-by: Danyao Wang <danyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614499}
11 files changed