[Android] Revert "Make the ResourceExtractor use the App context"

This reverts commit 0f1465d5fae40d3fd29b1c47e367eba488d7ef96.
For xwalk shared mode, the ResourceExtractor needs to read assets via Library Context
and write them to app data via App Context, so it must keep the original Context instead
of getting ApplicationContext of it.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1384
[Android] Address Context leak in ResourceExtractor

The leak is fixed by commit "Make the ResourceExtractor
use the App context"(0f1465d5f), which is reverted
because xwalk shared mode needs to keep original Context.

In this commit, the static instance of ResourceExtractor
will be released after the background job is done. The
ResourceExtractor should not be used any more from that point.
Add MessagePumpObserver for MessagePumpOzone.

A MessagePumpObserver is an object that receives global
notifications from the UI MessageLoop. It contains two APIs
WillProcessEvent() and DidProcessEvent(), so that observer could
do customized job before or after processing event in MessagePump.

Ozone-wayland implementation maps HW input as XKB key event and
supports to dispatch the event in Ozone message queue, while Crosswalk
doesn’t support fetching the event atm. A solution is to implement
the MessagePumpObserver APIs for OzoneMessagePump, so that Crosswalk
Runtime will be able to retrieve the HW key event.
Merge pull request #145 from wang16/resource_m35

[Android] Allow extracting resources across APKs
Merge pull request #144 from shaochangbin/observe-ozone-messagepump

[Tizen] Add MessagePumpObserver for MessagePumpOzone.