Occasionally fails with a resource deadlock:

[ RUN      ] BrowserCloseManagerWithBackgroundModeBrowserTest/BrowserCloseManagerWithBackgroundModeBrowserTest.CloseAllBrowsersWithBackgroundMode/1
[85759:43547:0726/225324.884101:WARNING:mac_util.mm(222)] Failed to set backup exclusion for file '/private/var/folders/9x/6c6sv3cj4j53wzpzthbp4ksm0000gm/T/.org.chromium.Chromium.qr4R9j/ds884Pc/Default/History': Error Domain=NSOSStatusErrorDomain Code=-50 "The operation couldn?t be completed. (OSStatus error -50.)" (paramErr: error in user parameter list) (-50)
[85759:5123:0726/225324.904780:WARNING:notification_platform_bridge_mac.mm(514)] AlertNotificationService: XPC connection invalidated.
[85759:43547:0726/225324.908250:WARNING:mac_util.mm(222)] Failed to set backup exclusion for file '/private/var/folders/9x/6c6sv3cj4j53wzpzthbp4ksm0000gm/T/.org.chromium.Chromium.qr4R9j/ds884Pc/Default/Favicons': Error Domain=NSOSStatusErrorDomain Code=-50 "The operation couldn?t be completed. (OSStatus error -50.)" (paramErr: error in user parameter list) (-50)
[85767:771:0726/225325.127979:WARNING:vt_video_decode_accelerator_mac.cc(178)] Failed to create VTDecompressionSession: Error Domain=NSOSStatusErrorDomain Code=-8973 "The operation couldn?t be completed. (OSStatus error -8973.)" (codecOpenErr) (-8973)
[85767:771:0726/225325.130117:WARNING:vt_video_decode_accelerator_mac.cc(200)] Failed to create hardware VideoToolbox session
[85767:771:0726/225325.215375:ERROR:vt_video_encode_accelerator_mac.cc(495)]  VTCompressionSessionCreate failed: -12908
[85759:771:0726/225325.788711:FATAL:lock_impl_posix.cc(63)] Check failed: rv == 0 (11 vs. 0). Resource deadlock avoided
0   libbase.dylib                       0x000000011f73e5ce base::debug::StackTrace::StackTrace(unsigned long) + 174
1   libbase.dylib                       0x000000011f73e69d base::debug::StackTrace::StackTrace(unsigned long) + 29
2   libbase.dylib                       0x000000011f73c93c base::debug::StackTrace::StackTrace() + 28
3   libbase.dylib                       0x000000011f7dbb9f logging::LogMessage::~LogMessage() + 479
4   libbase.dylib                       0x000000011f7d9505 logging::LogMessage::~LogMessage() + 21
5   libbase.dylib                       0x000000011f9a5d4e base::internal::LockImpl::Lock() + 270
6   libbase.dylib                       0x000000011f6d1773 base::Lock::Acquire() + 35
7   libbase.dylib                       0x000000011f6d1743 base::AutoLock::AutoLock(base::Lock&) + 35
8   libbase.dylib                       0x000000011f6d142d base::AutoLock::AutoLock(base::Lock&) + 29
9   libbase.dylib                       0x000000011f8c3c6b base::StatisticsRecorder::RegisterOrDeleteDuplicateRanges(base::BucketRanges const*) + 347
10  libbase.dylib                       0x000000011f898db4 base::PersistentHistogramAllocator::CreateHistogram(base::PersistentHistogramAllocator::PersistentHistogramData*) + 2948
11  libbase.dylib                       0x000000011f897e27 base::PersistentHistogramAllocator::GetHistogram(unsigned int) + 791
12  libbase.dylib                       0x000000011f897a4e base::PersistentHistogramAllocator::Iterator::GetNextWithIgnore(unsigned int) + 110
13  libbase.dylib                       0x000000011f8a132b base::GlobalHistogramAllocator::ImportHistogramsToStatisticsRecorder() + 91
14  libbase.dylib                       0x000000011f8c8828 base::StatisticsRecorder::ImportGlobalPersistentHistograms() + 56
15  libbase.dylib                       0x000000011f8c8e6f base::StatisticsRecorder::begin(bool) + 207
16  libbase.dylib                       0x000000011f8c9134 base::StatisticsRecorder::ValidateAllHistograms() + 84
17  browser_tests                       0x0000000107535107 SubprocessMetricsProvider::MergeHistogramDeltasFromAllocator(int, base::PersistentHistogramAllocator*) + 199
18  browser_tests                       0x00000001075342e3 SubprocessMetricsProvider::DeregisterSubprocessAllocator(int) + 1027
19  browser_tests                       0x0000000107537812 SubprocessMetricsProvider::RenderProcessExited(content::RenderProcessHost*, base::TerminationStatus, int) + 258
20  libcontent.dylib                    0x000000012ac41cae content::RenderProcessHostImpl::ProcessDied(bool, content::RenderProcessHost::RendererClosedDetails*) + 1822
21  libcontent.dylib                    0x000000012ac41360 content::RenderProcessHostImpl::FastShutdownIfPossible(unsigned long, bool) + 400
22  browser_tests                       0x000000010d0026fe TabStripModel::InternalCloseTabs(std::__1::vector<int, std::__1::allocator<int> > const&, unsigned int) + 1662
23  browser_tests                       0x000000010d002047 TabStripModel::CloseAllTabs() + 727
24  browser_tests                       0x000000010d4a501e -[BrowserWindowController windowShouldClose:] + 542
25  browser_tests                       0x000000010d49f357 BrowserWindowCocoa::Close() + 183
26  browser_tests                       0x00000001080b39e7 BrowserCloseManager::CloseBrowsers() + 1975
27  browser_tests                       0x00000001080b3ef5 BrowserCloseManager::CheckForDownloadsInProgress() + 21
28  browser_tests                       0x00000001080b3d13 BrowserCloseManager::TryToCloseBrowsers() + 371
29  browser_tests                       0x00000001080b3223 BrowserCloseManager::StartClosingBrowsers() + 67
30  browser_tests                       0x0000000107441fa7 chrome::CloseAllBrowsers() + 135
31  browser_tests                       0x00000001034f3d5b BrowserCloseManagerWithBackgroundModeBrowserTest_CloseAllBrowsersWithBackgroundMode_Test::RunTestOnMainThread() + 1003

on at least
chromium.mac/builders/Mac10.9%20Tests%20%28dbg%29/builds/43168
chromium.mac/builders/Mac10.9%20Tests%20%28dbg%29/builds/43161
chromium.mac/builders/Mac10.9%20Tests%20%28dbg%29/builds/43154
chromium.mac/builders/Mac10.9%20Tests%20%28dbg%29/builds/43151
chromium.mac/builders/Mac10.9%20Tests%20%28dbg%29/builds/43148
chromium.mac/builders/Mac10.9%20Tests%20%28dbg%29/builds/43146

The 26 runs before that were clear, so suspicion falls on changes in builds at or just before 46 ... more to come.