Chrome Version       : 55.0.2883.87
OS Version: ChromeOS (only)
URLs (if applicable) : 
Other browsers tested:
     Safari 5:
  Firefox 4.x:
     IE 7/8/9:

What steps will reproduce the problem?
1. In google3, run blaze run //research/colab/frontend/common/components:pinned_scroller_test_suite_debug
2. In Chrome OS, open browser to URL and run tests
3. The testStacking test fails

What is the expected result?
This particular test uses an IntersectionObserver with non-zero rootMargin to change the positioning of an element. The observer should trigger when one of the positioning elements is near the top of the scroll area.


What happens instead of that?
The intersection observer fires only when the area has been scrolled much further.

Please provide any additional information below. Attach a screenshot if
possible.

This functionality works as expected on Chrome 54/54 on Linux and OSX, but appears broken on ChromeOS.

UserAgentString: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36