Handle iOS devices with no rear-facing camera

webrtc/api/objc/avfoundationvideocapturer.h

 /*
  *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 22 matching lines @@
     return false;
   }
   bool GetPreferredFourccs(std::vector<uint32_t> *fourccs) override {
     fourccs->push_back(cricket::FOURCC_NV12);
     return true;
   }
 
   /** Returns the active capture session. */
   AVCaptureSession* GetCaptureSession();
 
+  /**
+   * Returns whether the rear-facing camera can be used.
+   * e.g. It can't be used because it doesn't exist.
+   */
+  bool CanUseBackCamera() const;
+
   /** Switches the camera being used (either front or back). */
   void SetUseBackCamera(bool useBackCamera);
   bool GetUseBackCamera() const;
 
   /**
    * Converts the sample buffer into a cricket::CapturedFrame and signals the
    * frame for capture.
    */
   void CaptureSampleBuffer(CMSampleBufferRef sampleBuffer);
 
  private:
   /**
    * Used to signal frame capture on the thread that capturer was started on.
    */
   void SignalFrameCapturedOnStartThread(const cricket::CapturedFrame *frame);
 
   RTCAVFoundationVideoCapturerInternal *_capturer;
   rtc::Thread *_startThread;  // Set in Start(), unset in Stop().
 };  // AVFoundationVideoCapturer
 
 }  // namespace webrtc
 
 #endif  // TALK_APP_WEBRTC_OBJC_AVFOUNDATION_CAPTURER_H_