Chrome Version: 05df6652b2b2717e8dbab651f4983b367903b7ec

What steps will reproduce the problem?
(1) Build with `dcheck_always_on = true`
(2) Drag a link.

What is the expected result?
No crash

What happens instead?
[55174:775:1031/123549.869567:FATAL:web_drag_source_mac.mm(102)] Check failed: pasteboard_.get().
0   libbase.dylib                       0x000000010f20f05c base::debug::StackTrace::StackTrace(unsigned long) + 28
1   libbase.dylib                       0x000000010f2397d2 logging::LogMessage::~LogMessage() + 210
2   libcontent.dylib                    0x0000000111f67887 -[WebDragSource initWithContents:view:dropData:sourceRWH:image:offset:pasteboard:dragOperationMask:] + 695
3   libcontent.dylib                    0x0000000111f64fb1 -[WebContentsViewCocoa startDragWithDropData:sourceRWH:dragOperationMask:image:offset:] + 241
4   libcontent.dylib                    0x0000000111f63f0b content::WebContentsViewMac::StartDragging(content::DropData const&, blink::WebDragOperation, gfx::ImageSkia const&, gfx::Vector2d const&, content::DragEventSourceInfo const&, content::RenderWidgetHostImpl*) + 155
5   libcontent.dylib                    0x0000000111dfde6e content::RenderWidgetHostImpl::OnStartDragging(content::DropData const&, blink::WebDragOperation, SkBitmap const&, gfx::Vector2d const&, content::DragEventSourceInfo const&) + 942
6   libcontent.dylib                    0x0000000111dfd9d1 bool IPC::MessageT<DragHostMsg_StartDragging_Meta, std::__1::tuple<content::DropData, blink::WebDragOperation, SkBitmap, gfx::Vector2d, content::DragEventSourceInfo>, void>::Dispatch<content::RenderWidgetHostImpl, content::RenderWidgetHostImpl, void, void (content::RenderWidgetHostImpl::*)(content::DropData const&, blink::WebDragOperation, SkBitmap const&, gfx::Vector2d const&, content::DragEventSourceInfo const&)>(IPC::Message const*, content::RenderWidgetHostImpl*, content::RenderWidgetHostImpl*, void*, void (content::RenderWidgetHostImpl::*)(content::DropData const&, blink::WebDragOperation, SkBitmap const&, gfx::Vector2d const&, content::DragEventSourceInfo const&)) + 193
7   libcontent.dylib                    0x0000000111dfa6b0 content::RenderWidgetHostImpl::OnMessageReceived(IPC::Message const&) + 1136
8   libcontent.dylib                    0x0000000111ddad9e content::RenderProcessHostImpl::OnMessageReceived(IPC::Message const&) + 494
9   libipc.dylib                        0x000000011049ca71 IPC::ChannelProxy::Context::OnDispatchMessage(IPC::Message const&) + 129
10  libipc.dylib                        0x000000011049f70b base::internal::Invoker<base::internal::BindState<void (IPC::ChannelProxy::Context::*)(IPC::Message const&), scoped_refptr<IPC::ChannelProxy::Context>, IPC::Message>, void ()>::Run(base::internal::BindStateBase*) + 139
11  libbase.dylib                       0x000000010f20f9e5 base::debug::TaskAnnotator::RunTask(char const*, base::PendingTask*) + 261
12  libbase.dylib                       0x000000010f250899 base::internal::IncomingTaskQueue::RunTask(base::PendingTask*) + 121
13  libbase.dylib                       0x000000010f255047 base::MessageLoop::RunTask(base::PendingTask*) + 551
14  libbase.dylib                       0x000000010f2554da base::MessageLoop::DeferOrRunPendingTask(base::PendingTask) + 202
15  libbase.dylib                       0x000000010f255761 base::MessageLoop::DoWork() + 593
16  libbase.dylib                       0x000000010f2595aa base::MessagePumpCFRunLoopBase::RunWork() + 42
17  libbase.dylib                       0x000000010f23b73a base::mac::CallWithEHFrame(void () block_pointer) + 10
18  libbase.dylib                       0x000000010f258e8f base::MessagePumpCFRunLoopBase::RunWorkSource(void*) + 63
19  CoreFoundation                      0x00007fffc87143e1 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
20  CoreFoundation                      0x00007fffc86f565c __CFRunLoopDoSources0 + 556
21  CoreFoundation                      0x00007fffc86f4b46 __CFRunLoopRun + 934
22  CoreFoundation                      0x00007fffc86f4544 CFRunLoopRunSpecific + 420
23  HIToolbox                           0x00007fffc7c53ebc RunCurrentEventLoopInMode + 240
24  HIToolbox                           0x00007fffc7c53cf1 ReceiveNextEventCommon + 432
25  HIToolbox                           0x00007fffc7c53b26 _BlockUntilNextEventMatchingListInModeWithFilter + 71
26  AppKit                              0x00007fffc61eca54 _DPSNextEvent + 1120
27  AppKit                              0x00007fffc69687ee -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 2796
28  libchrome_dll.dylib                 0x00000001070bb9f0 __71-[BrowserCrApplication nextEventMatchingMask:untilDate:inMode:dequeue:]_block_invoke + 64
29  libbase.dylib                       0x000000010f23b73a base::mac::CallWithEHFrame(void () block_pointer) + 10
30  libchrome_dll.dylib                 0x00000001070bb934 -[BrowserCrApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 164
31  AppKit                              0x00007fffc61e13db -[NSApplication run] + 926
32  libbase.dylib                       0x000000010f25a6d7 base::MessagePumpNSApplication::DoRun(base::MessagePump::Delegate*) + 359
33  libbase.dylib                       0x000000010f2588de base::MessagePumpCFRunLoopBase::Run(base::MessagePump::Delegate*) + 110
34  libbase.dylib                       0x000000010f254979 base::MessageLoop::Run(bool) + 169
35  libbase.dylib                       0x000000010f2930f8 base::RunLoop::Run() + 248
36  libchrome_dll.dylib                 0x00000001070c1708 ChromeBrowserMainParts::MainMessageLoopRun(int*) + 312
37  libcontent.dylib                    0x0000000111a010e4 content::BrowserMainLoop::RunMainMessageLoopParts() + 52
38  libcontent.dylib                    0x0000000111a04456 content::BrowserMainRunnerImpl::Run() + 102
39  libcontent.dylib                    0x00000001119fd42c content::BrowserMain(content::MainFunctionParams const&) + 124
40  libcontent.dylib                    0x00000001125d3084 content::ContentMainRunnerImpl::Run() + 564
41  libembedder.dylib                   0x000000010f0d7a72 service_manager::Main(service_manager::MainParams const&) + 2482
42  libcontent.dylib                    0x00000001125d2454 content::ContentMain(content::ContentMainParams const&) + 68
43  libchrome_dll.dylib                 0x0000000106806b6f ChromeMain + 175
44  Chromium                            0x0000000106799de4 main + 404
45  libdyld.dylib                       0x00007fffde2bf235 start + 1

CCing garykac@ in case it's related to recent DataTransfer changes.