React

• Add a new experimental React.unstable_Profiler component for measuring performance. (@bvaughn in #12745)

React DOM

• Add support for the Pointer Events specification. (@philipp-spiess in #12507)
• Properly call getDerivedStateFromProps() regardless of the reason for re-rendering. (@acdlite in #12600 and #12802)
• Fix a bug that prevented context propagation in some cases. (@gaearon in #12708)
• Fix re-rendering of components using forwardRef() on a deeper setState(). (@gaearon in #12690)
• Fix some attributes incorrectly getting removed from custom element nodes. (@airamrguez in #12702)
• Fix context providers to not bail out on children if there's a legacy context provider above. (@gaearon in #12586)
• Add the ability to specify propTypes on a context provider component. (@nicolevy in #12658)
• Fix a false positive warning when using react-lifecycles-compat in <StrictMode>. (@bvaughn in #12644)
• Warn when the forwardRef() render function has propTypes or defaultProps. (@bvaughn in #12644)
• Improve how forwardRef() and context consumers are displayed in the component stack. (@sophiebits in #12777)
• Change internal event names. This can break third-party packages that rely on React internals in unsupported ways. (@philipp-spiess in #12629)

React Test Renderer

• Fix the getDerivedStateFromProps() support to match the new React DOM behavior. (@koba04 in #12676)
• Fix a testInstance.parent crash when the parent is a fragment or another special node. (@gaearon in #12813)
• forwardRef() components are now discoverable by the test renderer traversal methods. (@gaearon in #12725)
• Shallow renderer now ignores setState() updaters that return null or undefined. (@koba04 in #12756)

React ART

• Fix reading context provided from the tree managed by React DOM. (@acdlite in #12779)

React Call Return (Experimental)

• This experiment was deleted because it was affecting the bundle size and the API wasn't good enough. It's likely to come back in the future in some other form. (@gaearon in #12820)

React Reconciler (Experimental)

• The new host config shape is flat and doesn't use nested objects. (@gaearon in #12792)