To reproduce:

1. Apply https://codereview.chromium.org/2786083005 (which slightly changes how delayed tasks are scheduled w.r.t. immediate tasks.)
2. python third_party/WebKit/Tools/Scripts/run-webkit-tests --debug fast/wasm/wasm-limits-test.html

crash log for renderer (pid <unknown>):
STDOUT: #CRASHED - renderer
STDERR: 
STDERR: 
STDERR: #
STDERR: # Fatal error in ../../v8/src/api.cc, line 217
STDERR: # Check failed: handle_scope_implementer->GetMicrotasksScopeDepth() || !handle_scope_implementer->DebugMicrotasksScopeDepthIsZero().
STDERR: #
STDERR: #0 0x0000019a6ac7 base::debug::StackTrace::StackTrace()
STDERR: #1 0x000002ff7f25 gin::(anonymous namespace)::PrintStackTrace()
STDERR: #2 0x000002d69a6d V8_Fatal
STDERR: #3 0x000000824b37 v8::(anonymous namespace)::CallDepthScope<>::~CallDepthScope()
STDERR: #4 0x00000083c362 v8::Function::Call()
STDERR: #5 0x000000fd9fe8 v8::(anonymous namespace)::WebAssemblyInstantiate()
STDERR: #6 0x0000008177ba v8::internal::FunctionCallbackArguments::Call()
STDERR: #7 0x0000008eaa37 v8::internal::(anonymous namespace)::HandleApiCallHelper<>()
STDERR: #8 0x0000008e93c2 v8::internal::Builtin_Impl_HandleApiCall()
STDERR: #9 0x034308884264 <unknown>
STDERR: [31059:31098:0412/032706.609182:7939432531:WARNING:crash_handler_host_linux.cc(325)] Could not translate tid, attempt = 1 retry ...

jochen@ suspected something is wrong with the processing of promises in wasm, so I'm planning to disable the tests in my patch.