Hi Sandra, could you let me know what it overscroll-behavior (and x/y variation) is like now for Android? 

I'm asking this because |root_overflow_y_hidden| in compositor_frame_metadata.h https://cs.chromium.org/chromium/src/components/viz/common/quads/compositor_frame_metadata.h?q=compositor_frame_meta&sq=package:chromium&g=0&l=156 seems always set to zero regardless of the presence of overscroll-behavior specified in css (same for x, for that matter). Is this a part of the issue you have in mind?

Currently, overscroll-behavior on Android controls the behavior of overscroll-refresh and overscroll-glow. https://cs.chromium.org/chromium/src/content/browser/android/overscroll_controller_android.cc?l=223

overscroll-behavior-y is none, no glow and no refresh
overscroll-behavior-y is contain, only glow and no refresh
overscroll-behacior-y is auto, glow or refresh depending on the behavior.

As we are working on OverscrollHistoryNavigation, we should implement overscroll-behavior-x for it as well. i.e. when overscroll-behavior-x is none, no navigation should happen.