[Windows] Implement the VideoCaptureDevicePxcWin based on PXCCapture API

PXCCapture is the Intel PCSDK API to access video streams including color
and depth streams on Windows OS.

VideoCaptureDevicePxcWin is the capture foundation to bring PerC capability
to Crosswalk. It serves:
- Capture color images for standard getUserMedia.
- Capture depth images for experimental 'depth' extension of getUserMedia.
- Avoid camera accessing confliction with the PerC Crosswalk Extensions.

To build it in, please install the Intel PCSDK and append gyp definition
"-Duse_pxc_capture=1" when generating the project.

BUG=
[Windows] Implement the 'depth' extension of getUserMedia

Web app is able to set 'depth' video mandatory constraint as
true to request a depth video capture via getUserMedia. e.g.

    getUserMedia(
        {video: {'mandatory': {'depth': true}},
        successCallback, errorCallback);

Currently, the depth image (16bit-per-pixel) is encoded into
RGB format.

There are three encoding options:
1. 'grayscale': convert depth image into 8-bit
   grayscale image. The algorithm is based on equation (4) in paper
   "3-D Video Representation Using Depth Maps".
2. 'adaptive': implement depth encoding scheme proposed in paper
   "Adapting Standard Video Codecs for Depth Streaming" [depth-streaming].
3. 'raw': map 16bit depth pixel into 3 8-bit channels which is based
   on BIT2 scheme in paper [depth-streaming].

Set the encoding schema via '--depth-encoding' switch.

Change-Id: Ied07b40ae487a15c7a2cfa23e3301028ec9afdaa
[Windows] Support RGB stream whose cooridnation is calibrated by depth

Web app is able to set 'depth' video mandatory constraint as
'rgbd' to request a RGB stream whose coordination is calibrated
by depth stream.

This RGB stream could be used as texture for depth-based rendering.

Change-Id: If14701237f415ca9a0c64ae6c2440c26b30b29fd