test(browser-integration): Allow built-in 'now' frame in profile validation

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Summary

The Playwright test traceLifecycleMode_overlapping-spans was flaky because validateProfile requires every captured frame (other than fetch/setTimeout/clearTimeout) to have an abs_path. When the JS Self Profiler samples while a built-in like Date.now() / performance.now() is on the stack, the resulting frame is { function: "now" } with no file location, causing expect(frame).toHaveProperty('abs_path') to fail.

Root cause

From the failing CI run:

Error: expect(received).toHaveProperty(path)
Expected path: "abs_path"
Received path: []
Received value: {"function": "now"}
   at profiling/test-utils.ts:104

now is another browser built-in without a JS source location, the same shape as the already-allowlisted fetch/setTimeout/clearTimeout. This adds now to the same allowlist.

Fixes #21114