[WiDi API] First commit for Presentation API implementation

This commit is the first patch to implement Presentation API spec which
is intended to bring wireless display support into Web. Since the spec
is still in Editor spec and might be changed in future, it is placed
under `navigator.experimental.presentation` namespace.

This patch mainly provides an mock implementation for display available
related API with several test cases. Next step is to add Android port
and requestShow API implementation.

SPEC=http://otcshare.github.io/presentation-spec/index.html

BUG=https://github.com/crosswalk-project/crosswalk/issues/577
TEST=xwalk_browsertest --gtest_filter=PresentationExtensionTest.*