Update XServerPixelBuffer to handle shmget() errors properly.

webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.cc

 /*
  *  Copyright (c) 2013 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 136 matching lines @@
         }
       }
     } else {
       LOG(LS_WARNING) << "Failed to get shared memory segment. "
                       "Performance may be degraded.";
     }
   }
 
   if (!using_shm) {
     LOG(LS_WARNING) << "Not using shared memory. Performance may be degraded.";
-    Release();
+    delete shm_segment_info_;
+    shm_segment_info_ = nullptr;

[Hzj_jie, 2017/03/25 00:30:30]

It looks like in Release() function, there are bunch of shm_segment_info_
cleanup statements, instead of just delete. And AFAICT, these fields are
initialized even when using_shm == false. I would suggest to abstract the
shm_segment_info_ cleanup logic into a standalone function and call it both here
and in Release().

[Sergey Ulanov, 2017/03/27 19:23:06]

Yes, good point. Fixed.
Also update this code to set shm_segment_info_->shmaddr and x_image_->data to
nullptr in unitialized state instead of -1 (shmat() returns (void*)-1 to
indicate error).

     return;
   }
 
   if (have_pixmaps)
     have_pixmaps = InitPixmaps(default_depth);
 
   shmctl(shm_segment_info_->shmid, IPC_RMID, 0);
   shm_segment_info_->shmid = -1;
 
   LOG(LS_VERBOSE) << "Using X shared memory extension v"
@@ skipping 163 matching lines @@
       // Write as 32-bit RGB.
       dst_pos_32[x] = ((r >> 8) & 0xff0000) | ((g >> 16) & 0xff00) |
           ((b >> 24) & 0xff);
     }
     dst_pos += frame->stride();
     src_pos += src_stride;
   }
 }
 
 }  // namespace webrtc