[Extensions] Add API for Check API Access Control

This API is for external extension developer. The API need to be called in the
implementation of each exported API in C or C++ code. For C extension
implantation, header file "public/XW_Extension_Permissions.h" should be
included. For each API that need access sensitive data, developer should call
CheckAPIAccessControl for API control. For C++ extension implantation, header
file "xwalk/common/xwalk_external_extension.h" should be included.

The basic flow of API access control is as below:
1. when render process execute a JS API which need access sensitive data
of device, render process send a message to extension process 2. in
extension process API's implemetation, it should call checkAPIAccessControl,
which will call PermissionsDelegate (which is in also extension process).
3. extension process send a message to browser process.
XWalkExtensionProcessHost -> XWalkExtensionProcessHost::Delegate (which
is XWalkExtensionService) -> XWalkExtensionService::Delegate (which is
XWalkBrowserMainParts) ->xwalk::application::ApplicationService::
CheckAPIAccessControl().

Conflicts:
	extensions/browser/xwalk_extension_service.h
	extensions/extensions.gypi
	runtime/browser/xwalk_browser_main_parts.cc
	runtime/browser/xwalk_browser_main_parts.h