Chrome Version       : 56.0.2914.3
OS Version: OS X 10.12.1

Bug to track a range of issues on macOS Sierra that have been triaged as an `ExternalDependency` due to inscrutable crashes.

Note this is a public bug, but the blocked-on issues may be restrict-view. So, leave a title or something useful in a comment if you add a blocker :)

Also I'm only considering Crashes/Hangs here (i.e. Not other things/glitches we've filed rdars for). It's possible some of these have been fixed by Apple, or at least fixed in the latest macOS but still biting us on older macOS versions.

First pass (in no particular order):
macOS Sierra specific:
 - Issue 668694: (concurrency issue in QuickLook) "Crash Report - [Cocoa Zombie] -[FI_TFlowView inlinePreview:frameForPreviewItem:]"
 -  Issue 654695 : "Using System IME Crashed on macOS Sierra" (rdar://29229715)
 -  Issue 653093 : SFChooseIdentityPanel (SSL certificate/credential selector leak) crash when manipulating displays "Sierra AppKit Crash: -[_NSTableRowHeightStorage numberOfRows]" (rdar://29409207)
 - Issue 661427: TouchBar crash in 10.12.2 Beta - hopefully fixed soon - "Crash Report - [Cocoa Zombie] -[NSAlert windowClosing:] (10.12.2 Beta)" rdar://29083312
 - Issue 667300: (NSXPCConnection crash - maybe Open/Save dialog) "Crash Report - [Cocoa Zombie] -[NSRemoteView connection:handleInvocation:isReply:]" (maybe resolved in 10.12.2?)

XPC stuff (more Open/Save dialogs?)  
  - Issue 511679: NSSavePanel crash: "Chrome crashes in _CSGetNamedData"
  -  Issue 428602 : NSXPCConnection/NSExtension "Chrome_Mac: Crash Report - _dispatch_barrier_async_f"


Other OS verisons
 - Issue 662900: (IME related?) Chrome_Mac: Crash Report - utTryToSetupInputMethodMenu (since 10.10 - no crashes on 10.9)
 - Issue 647116: "Chrome Hangs if coreaudiod is not responding"
 - Issue 620321: (Bug in Apple AVKit code) "[GPU hang] gpu::ImageTransportSurfaceOverlayMac::~ImageTransportSurfaceOverlayMac"
 - Issue 615845: (AVFoundation issue) "Crash: free_magazine"
 - Issue 543014: (crash in CarbonCore while creating a font in the renderer) "Chrome_Mac: Crash Report - blink::FontPlatformData::FontPlatformData"
 - Issue 532373: LSUserActivityManager crash? "Chrome_Mac: Crash Report - _CFPropertyListCopyShared under "_dispatch_worker_thread3" (system library)"
 - Issue 486392: (crash under gfx::GLFence::Create() at IOKit/io_connect_method) "Chrome Shutting Down Unexpectedly"
 -  Issue 274709 : "Chrome_Mac: Crash Report - Magic Signature: [Cocoa Exception] NSInvalidArgumentExceptio..." - has a rdar - maybe this is fixed..
 - Issue 160920: (old, but being worked on. Internal b/29521950 "Audio stops working on OSX and requires a browser restart to fix." (rdar://15485249)
 -  Issue 650882 : (rare crash under NSWindow _reallyDoOrderWindow) "Crash in ExclusiveAccessBubbleViews::AnimationProgressed(gfx::Animation const*) attempting to Show() the fullscreen bubble"
 - Issue 583049: (NSTextField substring glitches) "Crash when undoing a delete of a "/" that turns the address bar into a special URL handler"
 -  Issue 637270 : groups a bunch of crashes.  http://crbug.com/637270#c9  has a repro case for one "Crash: -[NSApplication _crashOnException:]"
 - Issue 520706: groups a bunch of crashes. "Chrome_Mac: Crash Report - __34-[BrowserCrApplication sendEvent:]_block_invoke [Needs better bucketing]" 
 - Issue 526263: groups a bunch of crashes. "Chrome_Mac: Crash Report - -[ChromeEventProcessingWindow sendEvent:]"