Pepper: Add IsAvailable() static methods to C++ wrappers to AudioInput_Dev and VideoCapture_Dev.

ppapi/cpp/dev/video_capture_dev.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PPAPI_CPP_DEV_VIDEO_CAPTURE_DEV_H_
 #define PPAPI_CPP_DEV_VIDEO_CAPTURE_DEV_H_
 
 #include "ppapi/c/dev/pp_video_capture_dev.h"
 #include "ppapi/cpp/resource.h"
 
 namespace pp {
 
 class Instance;
 
 class VideoCapture_Dev : public Resource {
  public:
   explicit VideoCapture_Dev(const Instance& instance);
   VideoCapture_Dev(PP_Resource resource);
   VideoCapture_Dev(const VideoCapture_Dev& other);
 
+  // Returns true if the required interface is available.
+  static bool IsAvailable();
+
   int32_t StartCapture(const PP_VideoCaptureDeviceInfo_Dev& requested_info,
                        uint32_t buffer_count);
   int32_t ReuseBuffer(uint32_t buffer);
   int32_t StopCapture();
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_DEV_VIDEO_CAPTURE_DEV_H_