Remove modules/webdatabase dependency from core.

This CL introduces ActiveDOMObject::willStop, and moves Web Database stuff in
WorkerThread into DatabaseContext::willStop.

BUG=none
TEST=none; no behavior changes.

Review URL: https://codereview.chromium.org/196543003

git-svn-id: svn://svn.chromium.org/blink/trunk@169068 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move history load deferral handling from HistoryController to FrameLoader

Deferred loading is a blink concept, and HistoryController is leaving blink
soon.

BUG=none

Review URL: https://codereview.chromium.org/179863005

git-svn-id: svn://svn.chromium.org/blink/trunk@169069 bbb929c8-8fbe-4397-9dbb-9b2b20218538