recalculate dpi on different platform

The scale factor will always be 1 if the output scale does not change.
So I default set factor to 1. If the event happens, the listener will
get the scale.
Merge pull request #356 from scuxiayiqian/recalculate-dpi

recalculate dpi on different platform
Bump version to 0.87
Upgrade after crosswalk always use tizen_app_id on tizen,
fix cannot get current app info and dbus proxy.

PR#2261 : https://github.com/crosswalk-project/crosswalk/pull/2261

After PR#2261, we always get the app_id which will equal to the
app_id storaged in pkgmgr DB, so there is no need to convert
pkg_id to app_id.

Because object path with '.' is an invalid object path, so
after PR#2261 the object path of running application on dbus
was changed so we need to change it too.

BUG=XWALK-1925
Merge pull request #361 from CooderIan/upgrade_app_id

Upgrade after crosswalk always use tizen_app_id on tizen, fix cannot get current app info and dbus proxy.
[Download] Fix and complete Download API

Refactored Filesytem and Download API to share code
related to virtual roots.
Pass TCT tests.
Fix example.

BUG=XWALK-1070