See https://codereview.chromium.org/12089071/diff/1004/runtime/vm/dart_api_impl.cc?column_width=80 for then implementation which causes this ASSERT in debug mode:

#­0 0xf7fdb430 in __kernel_vsyscall ()
#­1 0xf7ce41df in raise () from /lib/i386-linux-gnu/libc.so.6
#­2 0xf7ce7825 in abort () from /lib/i386-linux-gnu/libc.so.6
#­3 0x080a5484 in dart::DynamicAssertionHelper::Fail (this=0xf35fe1ec,
    format=0x85e9f75 "expected: %s") at runtime/platform/assert.cc:40
#­4 0x081438bb in dart::Handles<2, 64, 4>::VerifyScopedHandleState (
    this=0xf35fef50) at runtime/vm/handles_impl.h:267
#­5 0x08142fa9 in dart::HandleScope::HandleScope (this=0xf35fe448,
    __in_chrg=<optimized out>) at runtime/vm/handles.cc:102
#­6 0x080ec56e in dart::JumpToExceptionHandler (program_counter=4085139106,
    stack_pointer=4083148320, frame_pointer=4083148368, exception_object=...,
    stacktrace_object=...) at runtime/vm/exceptions.cc:135
#­7 0x080ec9b2 in dart::ThrowExceptionHelper (incoming_exception=...,
    existing_stacktrace=...) at runtime/vm/exceptions.cc:227
#­8 0x080ed1d0 in dart::Exceptions::Throw (exception=...)
    at runtime/vm/exceptions.cc:380
#­9 0x0806c109 in dart::ThrowArgumentError (
    exception_message=0x85d1128 "List contains non-int elements")
    at runtime/vm/dart_api_impl.cc:2105
#­10 0x0806c62f in dart::Dart_ListGetAsBytes (list=0xf3300db4, offset=0,
    native_array=0xf3300ac0 "\001\002\003\363\020\001\060\363\300T\bM",
    length=4) at runtime/vm/dart_api_impl.cc:2157
#­11 0x080addf2 in Builtin_Socket_WriteList (args=0xf35fe584)
    at runtime/bin/socket.cc:208
#­12 0xf5bc015e in ?? ()
#­13 0xf37e607d in ?? ()
#­14 0xf37e5960 in ?? ()
#­15 0xf37e54a7 in ?? ()
#­16 0xf37e5381 in ?? ()
#­17 0xf37e4494 in ?? ()
#­18 0xf37e4263 in ?? ()
#­19 0xf37dea86 in ?? ()
#­20 0xf37de8ef in ?? ()
#­21 0xf37de5f7 in ?? ()
#­22 0xf37de509 in ?? ()
#­23 0xf37dddb0 in ?? ()
#­24 0xf37ddb09 in ?? ()
#­25 0xf37e416f in ?? ()
#­26 0xf37e407d in ?? ()
#­27 0xf37e3f39 in ?? ()
#­28 0xf37e1fe7 in ?? ()
#­29 0xf37d4b5c in ?? ()
#­30 0xf37d4834 in ?? ()
#­31 0xf37d6567 in ?? ()
#­32 0xf37d4b80 in ?? ()
#­33 0xf37d4834 in ?? ()
#­34 0xf37d6567 in ?? ()
#­35 0xf37d4b80 in ?? ()
#­36 0xf37d4834 in ?? ()
#­37 0xf37d45fa in ?? ()
#­38 0xf37e19fe in ?? ()
#­39 0xf37dce7b in ?? ()
#­40 0xf37dc81b in ?? ()
#­41 0xf37d4279 in ?? ()
#­42 0xf37c0078 in ?? ()
#­43 0x080d94d4 in dart::DartEntry::InvokeStatic (function=..., arguments=...,
    arguments_descriptor=...) at runtime/vm/dart_entry.cc:88
#­44 0x080d9321 in dart::DartEntry::InvokeStatic (function=..., arguments=...)

Removed Priority-Medium label.
Added Priority-Unassigned label.

Some of the corresponding API code has been cleaned in the meantime.