Fix DesktopSessioAgent crash when handling nullptr OnCaptureCompleted callback.

remoting/host/desktop_session_agent.cc

 // 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.
 
 #include "remoting/host/desktop_session_agent.h"
 
 #include <utility>
 
 #include "base/files/file_util.h"
 #include "base/logging.h"
@@ skipping 308 matching lines @@
           base::Bind(&DesktopSessionAgent::SendToNetwork, this))));
   mouse_cursor_monitor_ = desktop_environment_->CreateMouseCursorMonitor();
   mouse_cursor_monitor_->Init(this, webrtc::MouseCursorMonitor::SHAPE_ONLY);
 }
 
 void DesktopSessionAgent::OnCaptureCompleted(webrtc::DesktopFrame* frame) {
   DCHECK(caller_task_runner_->BelongsToCurrentThread());
 
   last_frame_.reset(frame);
 
-  current_size_ = frame->size();
-
   // Serialize webrtc::DesktopFrame.
   SerializedDesktopFrame serialized_frame;
-  serialized_frame.shared_buffer_id = frame->shared_memory()->id();
-  serialized_frame.bytes_per_row = frame->stride();
-  serialized_frame.dimensions = frame->size();
-  serialized_frame.capture_time_ms = frame->capture_time_ms();
-  serialized_frame.dpi = frame->dpi();
-  for (webrtc::DesktopRegion::Iterator i(frame->updated_region());
-       !i.IsAtEnd(); i.Advance()) {
-    serialized_frame.dirty_region.push_back(i.rect());
+  if (frame) {
+    serialized_frame.shared_buffer_id = frame->shared_memory()->id();
+    serialized_frame.bytes_per_row = frame->stride();
+    serialized_frame.dimensions = frame->size();
+    serialized_frame.capture_time_ms = frame->capture_time_ms();
+    serialized_frame.dpi = frame->dpi();
+    for (webrtc::DesktopRegion::Iterator i(frame->updated_region());
+         !i.IsAtEnd(); i.Advance()) {
+      serialized_frame.dirty_region.push_back(i.rect());
+    }
   }
 
   SendToNetwork(base::WrapUnique(
       new ChromotingDesktopNetworkMsg_CaptureCompleted(serialized_frame)));
 }
 
 void DesktopSessionAgent::OnMouseCursor(webrtc::MouseCursor* cursor) {
   DCHECK(caller_task_runner_->BelongsToCurrentThread());
 
   std::unique_ptr<webrtc::MouseCursor> owned_cursor(cursor);
@@ skipping 227 matching lines @@
   }
 }
 
 void DesktopSessionAgent::StopAudioCapturer() {
   DCHECK(audio_capture_task_runner_->BelongsToCurrentThread());
 
   audio_capturer_.reset();
 }
 
 }  // namespace remoting