Add a CHECK to ScriptValueToObject

Change a DCHECK in blink::ScriptValueToObject() to a CHECK as I think
this condition is probably failing in the wild and I want to confirm.

BUG=1052314

Change-Id: I4f53e8b9b7d3ca033e56103e2a110013f6e73df1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2067768Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745357}

third_party/blink/renderer/core/streams/miscellaneous_operations.cc

@@ -485,7 +485,7 @@ void ScriptValueToObject(ScriptState* script_state,
                          v8::Local<v8::Object>* object,
                          ExceptionState& exception_state) {
   auto* isolate = script_state->GetIsolate();
-  DCHECK(!value.IsEmpty());
+  CHECK(!value.IsEmpty());
   auto v8_value = value.V8Value();
   // All the object parameters in the standard are default-initialised to an
   // empty object.