This test triggers a shutdown crash in mash:

#0  0x00007ffff279bde3 in wm::FocusController::SetFocusedWindow (this=0x8da611a4020, window=0x0) at ../../ui/wm/core/focus_controller.cc:256
#1  0x00007ffff279b7ba in wm::FocusController::FocusAndActivateWindow (this=0x8da611a4020, reason=aura::client::ActivationChangeObserver::ActivationReason::ACTIVAT\
ION_CLIENT, window=0x0) at ../../ui/wm/core/focus_controller.cc:220
#2  0x00007ffff279b461 in wm::FocusController::FocusWindow (this=0x8da611a4020, window=0x0) at ../../ui/wm/core/focus_controller.cc:105
#3  0x00007ffff61966f1 in ash::Shell::~Shell (this=0x8da61047320) at ../../ash/shell.cc:428
#4  0x00007ffff6197a39 in ash::Shell::~Shell (this=0x8da61047320) at ../../ash/shell.cc:415
#5  0x00007ffff6194a1d in ash::Shell::DeleteInstance () at ../../ash/shell.cc:213
#6  0x000000000072c641 in ash::mus::WindowManager::Shutdown (this=0x8da611eac20) at ../../ash/mus/window_manager.cc:256
#7  0x000000000072c4b5 in ash::mus::WindowManager::~WindowManager (this=0x8da611eac20) at ../../ash/mus/window_manager.cc:80
#8  0x000000000072c6d9 in ash::mus::WindowManager::~WindowManager (this=0x8da611eac20) at ../../ash/mus/window_manager.cc:79
#9  0x00000000005c86d2 in std::default_delete<ash::mus::WindowManager>::operator() (this=0x8da611d1968, __ptr=0x8da611eac20) at ../../build/linux/ubuntu_precise_am\
d64-sysroot/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/bits/unique_ptr.h:63
#10 0x00000000005c699c in std::unique_ptr<ash::mus::WindowManager, std::default_delete<ash::mus::WindowManager> >::reset (this=0x8da611d1968, __p=0x8da611eac20) at\
 ../../build/linux/ubuntu_precise_amd64-sysroot/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/bits/unique_ptr.h:245
#11 0x00000000007398e8 in ash::mus::WindowManagerApplication::~WindowManagerApplication (this=0x8da611d18e0) at ../../ash/mus/window_manager_application.cc:44
#12 0x0000000000739a49 in ash::mus::WindowManagerApplication::~WindowManagerApplication (this=0x8da611d18e0) at ../../ash/mus/window_manager_application.cc:41
#13 0x000000000048bbef in std::default_delete<mash::test::TestContextFactory>::operator() (this=0x8da611d24c8, __ptr=0x8da611d18e0) at ../../build/linux/ubuntu_pre\
cise_amd64-sysroot/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/bits/unique_ptr.h:63
#14 0x00000000005c64ec in std::unique_ptr<ash::mus::WindowManagerApplication, std::default_delete<ash::mus::WindowManagerApplication> >::reset (this=0x8da611d24c8,\
 __p=0x8da611d18e0) at ../../build/linux/ubuntu_precise_amd64-sysroot/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/bits/unique_ptr.h:245
#15 0x00000000009b902d in ash::test::AshTestHelper::TearDown (this=0x8da611d2480) at ../../ash/test/ash_test_helper.cc:173
#16 0x00000000009b6bb6 in ash::test::AshTestBase::TearDown (this=0x8da6111af70) at ../../ash/test/ash_test_base.cc:158
#17 0x00000000009f6cbe in testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void> (object=0x8da6111af70, method=&virtual testing::Test::Tear\
Down(), location=0xc39318 "TearDown()") at ../../testing/gtest/src/gtest.cc:2402


I'm tagging this with mustash-1 as shutdown crashes generally indicate bad code that is likely to bite us sooner rather than later. The test does fail though, so it's possible the badness is entirely in the test, but we should understand that.