Return early for child same origin frames

If we have cross origin record turned on but we are in a child
frame that has the same origin as its parent we end up in sort
of an inefficient state. We will start the recording, record
mutations, but then never actually emit them anywhere since
inEmittingFrame and passEmitsToParent are both false. This
is a waste of resources and we might as well just never start
the recording.

packages/rrweb/src/record/index.ts

@@ -108,6 +108,11 @@ function record<T = eventWithTime>(
   if (inEmittingFrame && !emit) {
     throw new Error('emit function is required');
   }
+  if (!inEmittingFrame && !passEmitsToParent) {
+    return () => {
+      /* no-op since in this case we don't need to record anything from this frame in particular */
+    };
+  }
   // move departed options to new options
   if (mousemoveWait !== undefined && sampling.mousemove === undefined) {
     sampling.mousemove = mousemoveWait;