Overall permission bubble looks awesome. One crash:

Steps to repro:

1. Run Chromium with HBD
2. Go to http://pps-test-a.appspot.com/small_only.html
3. Click Download flash link
4. Observe Permission bubble for Flash opening
5. Click X to close that permission bubble
6. Crash below.

tommycli@tommycli:~/src/chromium/src$ ninja -j2000 -l30 -C out/rel chrome && out/rel/chrome --ppapi-flash-path=$PPAPI_FLASH_PATH --enable-features="PreferHtmlOverPlugins<PreferHtmlOverPlugins" --force-fieldtrials=PreferHtmlOverPlugins/Enabled --force-fieldtrial-params=PreferHtmlOverPlugins.Enabled:engagement_threshold_for_flash/100
ninja: Entering directory `out/rel'
ninja: no work to do.
[WARNING:flash/platform/pepper/pep_module.cpp(63)] SANDBOXED
Vector smash protection is enabled.
[30970:30970:0927/141044:FATAL:permission_manager.cc(68)] Check failed: false. 
#0 0x7fd217d8186e base::debug::StackTrace::StackTrace()
#1 0x7fd217da3a7b logging::LogMessage::~LogMessage()
#2 0x7fd218ce684f (anonymous namespace)::ContentSettingToPermissionStatusCallbackWrapper()
#3 0x7fd218b8731f PermissionContextBase::NotifyPermissionSet()
#4 0x7fd218b86fdd PermissionContextBase::PermissionDecided()
#5 0x7fd218b8782c _ZN4base8internal7InvokerINS0_9BindStateIM21PermissionContextBaseFvRK19PermissionRequestIDRK4GURLS9_bRKNS_8CallbackIFv14ContentSettingELNS0_8CopyModeE1ELNS0_10RepeatModeE1EEEbSB_EJNS_7WeakPtrIS3_EES4_S7_S7_bSF_EEEFvbSB_EE3RunEPNS0_13BindStateBaseEObOSB_
#6 0x7fd218b88888 PermissionRequestImpl::Cancelled()
#7 0x7fd218b8a7fc PermissionRequestManager::CancelledIncludingDuplicates()
#8 0x7fd218b8a8fb PermissionRequestManager::Closing()
#9 0x7fd219994a2d PermissionsBubbleDialogDelegateView::OnWidgetDestroying()
#10 0x7fd2134c6974 views::Widget::OnNativeWidgetDestroying()
#11 0x7fd2134dcc91 views::NativeWidgetAura::OnWindowDestroying()
#12 0x7fd213570c03 aura::Window::~Window()
#13 0x7fd213571689 aura::Window::~Window()
#14 0x7fd217d82394 base::debug::TaskAnnotator::RunTask()
#15 0x7fd217daf0f5 base::MessageLoop::RunTask()
#16 0x7fd217daf498 base::MessageLoop::DeferOrRunPendingTask()
#17 0x7fd217daf8bb base::MessageLoop::DoWork()
#18 0x7fd217db177a base::(anonymous namespace)::WorkSourceDispatch()
#19 0x7fd2117b0e04 g_main_context_dispatch
#20 0x7fd2117b1048 <unknown>
#21 0x7fd2117b10ec g_main_context_iteration
#22 0x7fd217db14d6 base::MessagePumpGlib::Run()
#23 0x7fd217daebf1 base::MessageLoop::RunHandler()
#24 0x7fd217ddc510 base::RunLoop::Run()
#25 0x7fd218dea51a ChromeBrowserMainParts::MainMessageLoopRun()
#26 0x7fd2159453c9 content::BrowserMainLoop::RunMainMessageLoopParts()
#27 0x7fd215948670 content::BrowserMainRunnerImpl::Run()
#28 0x7fd215940bfe content::BrowserMain()
#29 0x7fd21626cbbe content::RunNamedProcessTypeMain()
#30 0x7fd21626d61b content::ContentMainRunnerImpl::Run()
#31 0x7fd21626beb0 content::ContentMain()
#32 0x7fd2187f756d ChromeMain
#33 0x7fd20edb7f45 __libc_start_main
#34 0x7fd2187f743d <unknown>

Aborted (core dumped)