Hybrid Overscroll: Root Glow and Inner Bounce in WebView

The provided text details the complex mechanisms governing overscroll behavior within the Android WebView and Chromium engine, specifically contrasting how the root content and non-root scrollable elements display boundary feedback. For the root content, WebView intentionally disables Chromium's built-in elastic bounce and instead funnels overscroll events to the Java layer, where the native Android EdgeEffect API draws a standard edge glow unless the app developer explicitly disables it. Conversely, a feature flag called OverscrollEffectOnNonRootScrollers enables an elastic, rubber-band bounce effect for inner scrollable components, which is achieved entirely via compositor transforms handled by the ElasticOverscrollController and InputHandlerProxy within Chromium, ensuring the root glow and inner bounce can coexist without conflict. This design establishes a hybrid overscroll model that preserves the expected Android look for the main view while providing advanced web functionality for internal scrollers.