handle the case when device is closed before media pipeline is fully initialized.

media/video/capture/video_capture_device.h

 // Copyright (c) 2012 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.
 //
 // VideoCaptureDevice is the abstract base class for realizing video capture
 // device support in Chromium. It provides the interface for OS dependent
 // implementations.
 // The class is created and functions are invoked on a thread owned by
 // VideoCaptureManager. Capturing is done on other threads depended on the OS
 // specific implementation.
@@ skipping 16 matching lines @@
   struct Name {
     // Friendly name of a device
     std::string device_name;
 
     // Unique name of a device. Even if there are multiple devices with the same
     // friendly name connected to the computer this will be unique.
     std::string unique_id;
   };
   typedef std::list<Name> Names;
 
-  class EventHandler {
+  class MEDIA_EXPORT EventHandler {
    public:
     // Captured a new video frame.
     virtual void OnIncomingCapturedFrame(const uint8* data,
                                          int length,
                                          base::Time timestamp) = 0;
     // An error has occurred that can not be handled
     // and VideoCaptureDevice must be DeAllocated.
     virtual void OnError() = 0;
     // Called when VideoCaptureDevice::Allocate has been called
     // to inform of the resulting frame size and color format.
@@ skipping 31 matching lines @@
   // state it was when created.
   virtual void DeAllocate() = 0;
 
   // Get the name of the capture device.
   virtual const Name& device_name() = 0;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_VIDEO_CAPTURE_VIDEO_CAPTURE_DEVICE_H_