Fixed partially out of screen window capture in unix

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 bcfcb7e02792a86c940852aab545d1783f7b329d..b99763950ef77e52d6f6dd942947bce0e1b2bf6d 100644
--- a/webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.cc
+++ b/webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.cc
@@ -59,11 +59,7 @@ bool IsXImageRGBFormat(XImage* image) {
 
 namespace webrtc {
 
-XServerPixelBuffer::XServerPixelBuffer()
-    : display_(NULL), window_(0),
-      x_image_(NULL),
-      shm_segment_info_(NULL), shm_pixmap_(0), shm_gc_(NULL) {
-}
+XServerPixelBuffer::XServerPixelBuffer() {}
 
 XServerPixelBuffer::~XServerPixelBuffer() {
   Release();
@@ -229,7 +225,9 @@ void XServerPixelBuffer::Synchronize() {
   if (shm_segment_info_ && !shm_pixmap_) {
     // XShmGetImage can fail if the display is being reconfigured.
     XErrorTrap error_trap(display_);
-    XShmGetImage(display_, window_, x_image_, 0, 0, AllPlanes);
+    // XShmGetImage fails if the window is partially out of screen.
+    xshm_get_image_succeeded_ =
+        XShmGetImage(display_, window_, x_image_, 0, 0, AllPlanes);
   }
 }
 
@@ -240,7 +238,7 @@ void XServerPixelBuffer::CaptureRect(const DesktopRect& rect,
 
   uint8_t* data;
 
-  if (shm_segment_info_) {
+  if (shm_segment_info_ && (shm_pixmap_ || xshm_get_image_succeeded_)) {
     if (shm_pixmap_) {
       XCopyArea(display_, window_, shm_pixmap_, shm_gc_,
                 rect.left(), rect.top(), rect.width(), rect.height(),