[Android] Set DIP scale and refine the parameter.

This patch is to set the DIP scale in the construction of XWalkContent
and refine the parameter of onScaleChanged().
[Android] Add test case for OnScaleChanged.

This patch is to add test case for OnScaleChanged().
[Android][SysApps] Make StorageUnit.id and DisplayUnit.id be type of string.

BUG=XWALK-2354
Merge pull request #2314 from wuhengzhi/onScaleChanged_test

[Android] Set DIP scale and add test case for onScaleChanged.
Merge pull request #2324 from legendlee1314/cleanfails

[Android][SysApps] Make StorageUnit.id and DisplayUnit.id be type of string.
[Android] Enable reflection layer generator

Add a python script to generating code for classes in
org.xwalk.core from classes in org.xwalk.core.internal
which need to be exposed in Embedding API.

For each class of org.xwalk.core.internal which needs to be
exposed in Embedding API.
A bridge class and a wrapper class will be created for it.
The bridge class is a subclass of internal class and maintains
a wrapper object of this type.
A wrapper class is in org.xwalk.core and be exposed in Embedding
API, it maintains an instance of bridge object as well.
Wrapper and bridge talks to each other via pure reflection. So
they don't have to be in the same package in future.

TODO: JavascriptInterface class needs to be placed in wrapper and
pass the class object to internal for recognition of javascript
interface.

BUG Related: https://crosswalk-project.org/jira/browse/XWALK-1638
Merge pull request #2251 from wang16/reflection_layer

[Android] Use script to generate core code which is a simple wrap of core internal
[Tizen] Implement "xwalkctl -d PORT_NUMBER" to
dynamically enable remote debugging mode

With this patch, to enable remote debugging, we don't need to modify the
configure file "/usr/lib/systemd/user/xwalk.service" and restart the xwalk
service anymore.

Usage:
xwalkctl -d 9222   #enabled remote debugging at port '9222'
xwalkctl -d 0      #disable remote debugging

BUG=https://crosswalk-project.org/jira/browse/XWALK-2058