[tooling] Keep track of idle state even when we aren't profiling

It isn't expensive to set this enum on the isolate and we only call
this in chrome when the ThreadDebugger is enabled anyway.

This means we have a correct idle state to use with the upcoming
CDP event which emits the thread state.

Bug: chromium:1025490
Change-Id: Ia555ac8c401d0ad7c72d4cbc442be388ce166131
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2036087Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66125}

src/execution/isolate.cc

@@ -4362,7 +4362,6 @@ void Isolate::PrintWithTimestamp(const char* format, ...) {
 }
 
 void Isolate::SetIdle(bool is_idle) {
-  if (!is_profiling()) return;
   StateTag state = current_vm_state();
   DCHECK(state == EXTERNAL || state == IDLE);
   if (js_entry_sp() != kNullAddress) return;