(lldb) bt 20
* thread #31, name = 'TaskSchedulerForegroundBlockingWorker', stop reason = EXC_BREAKPOINT (code=EXC_I386_BPT, subcode=0x0)
  * frame #0: 0x000000010bfcd024 Google Chrome Framework`base::debug::BreakDebugger() at debugger_posix.cc:269
    frame #1: 0x000000010bceee02 Google Chrome Framework`logging::LogMessage::~LogMessage(this=0x000070000f756030) at logging.cc:855
    frame #2: 0x000000010bce5e15 Google Chrome Framework`logging::LogMessage::~LogMessage(this=0x000070000f756030) at logging.cc:586
    frame #3: 0x000000010beef87c Google Chrome Framework`base::internal::AssertBaseSyncPrimitivesAllowed() at thread_restrictions.cc:105
    frame #4: 0x000000010be6b3ca Google Chrome Framework`base::WaitableEvent::TimedWaitUntil(this=0x000000015321df68, end_time=0x000070000f756410) at waitable_event_mac.cc:114
    frame #5: 0x000000010be6b7fb Google Chrome Framework`base::WaitableEvent::TimedWait(this=0x000000015321df68, wait_delta=0x000070000f756460) at waitable_event_mac.cc:110
    frame #6: 0x0000000103fc37fb Google Chrome Framework`rtc::Event::Wait(this=0x000000015321df68, milliseconds=10000) at event.cc:35
    frame #7: 0x0000000112f82538 Google Chrome Framework`webrtc::EventWrapperImpl::Wait(this=0x000000015321df60, max_time=10000) at event.cc:43
    frame #8: 0x0000000112f628f6 Google Chrome Framework`webrtc::DesktopConfigurationMonitor::Lock(this=0x000000014ff3c770) at desktop_configuration_monitor.cc:45
    frame #9: 0x0000000104c80599 Google Chrome Framework`webrtc::ScreenCapturerMac::CaptureFrame(this=0x000000014c00b680) at screen_capturer_mac.mm:268
    frame #10: 0x000000010abbea2c Google Chrome Framework`NativeDesktopMediaList::Worker::RefreshThumbnails(this=0x000000014d980550, native_ids=size=1, thumbnail_size=0x000000014c076b20) at native_desktop_media_list.cc:172

 

(lldb) bt 20
* thread #31, name = 'TaskSchedulerForegroundBlockingWorker', stop reason = EXC_BREAKPOINT (code=EXC_I386_BPT, subcode=0x0)
  * frame #0: 0x000000010bfcd024 Google Chrome Framework`base::debug::BreakDebugger() at debugger_posix.cc:269
    frame #1: 0x000000010bceee02 Google Chrome Framework`logging::LogMessage::~LogMessage(this=0x000070000f756030) at logging.cc:855
    frame #2: 0x000000010bce5e15 Google Chrome Framework`logging::LogMessage::~LogMessage(this=0x000070000f756030) at logging.cc:586
    frame #3: 0x000000010beef87c Google Chrome Framework`base::internal::AssertBaseSyncPrimitivesAllowed() at thread_restrictions.cc:105
    frame #4: 0x000000010be6b3ca Google Chrome Framework`base::WaitableEvent::TimedWaitUntil(this=0x000000015321df68, end_time=0x000070000f756410) at waitable_event_mac.cc:114
    frame #5: 0x000000010be6b7fb Google Chrome Framework`base::WaitableEvent::TimedWait(this=0x000000015321df68, wait_delta=0x000070000f756460) at waitable_event_mac.cc:110
    frame #6: 0x0000000103fc37fb Google Chrome Framework`rtc::Event::Wait(this=0x000000015321df68, milliseconds=10000) at event.cc:35
    frame #7: 0x0000000112f82538 Google Chrome Framework`webrtc::EventWrapperImpl::Wait(this=0x000000015321df60, max_time=10000) at event.cc:43
    frame #8: 0x0000000112f628f6 Google Chrome Framework`webrtc::DesktopConfigurationMonitor::Lock(this=0x000000014ff3c770) at desktop_configuration_monitor.cc:45
    frame #9: 0x0000000104c80599 Google Chrome Framework`webrtc::ScreenCapturerMac::CaptureFrame(this=0x000000014c00b680) at screen_capturer_mac.mm:268
    frame #10: 0x000000010abbea2c Google Chrome Framework`NativeDesktopMediaList::Worker::RefreshThumbnails(this=0x000000014d980550, native_ids=size=1, thumbnail_size=0x000000014c076b20) at native_desktop_media_list.cc:172

(lldb) print *pending_task
(base::PendingTask) $1 = {
  task = {
    base::internal::CallbackBase = {
      bind_state_ = {
        ptr_ = 0x0000000000000000
      }
    }
  }
  posted_from = {
    function_name_ = 0x000000011db03736 "RefreshForAuraWindows"
    file_name_ = 0x000000011db036cb "./../../chrome/browser/media/webrtc/native_desktop_media_list.cc"
    line_number_ = 284
    program_counter_ = 0x000000010abbe692
  }
  delayed_run_time = {
    base::time_internal::TimeBase<base::TimeTicks> = (us_ = 0)
  }
  task_backtrace = {
    __elems_ = ([0] = 0x000000010abbe010, [1] = 0x000000010abc02f1, [2] = 0x000000010c67a578, [3] = "eeeeioiB9")
  }
  sequence_num = 3487
  nestable = kNonNestable
  is_high_res = false
}