Update XServerPixelBuffer to handle shmget() errors properly.

webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.cc

Index: webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.cc
diff --git a/webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.cc b/webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.cc
index 2ecac6b8b0321c87da9645770942fd9f827507c9..522e688a8d0f91f3a3ac365dfa0a09774bee2fdc 100644
--- a/webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.cc
+++ b/webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.cc
@@ -154,7 +154,8 @@ void XServerPixelBuffer::InitShm(const XWindowAttributes& attributes) {
 
   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;
   }