Add ctx._context for backwards compat

Author: gaearon

packages/react/src/ReactContext.js

@@ -30,6 +30,8 @@ export function createContext<T>(defaultValue: T): ReactContext<T> {
     // These are circular
     Provider: (null: any),
     Consumer: (null: any),
+    // Temporary for backwards compat:
+    _context: null,
   };
 
   context.Provider = context;
@@ -38,6 +40,10 @@ export function createContext<T>(defaultValue: T): ReactContext<T> {
     _context: context,
   };
 
+  // Some tooling (e.g. DevTools) may assume that context.Provider._context === context.
+  // Keep that true for now to avoid excessive breakage.
+  context._context = context;
+
   if (__DEV__) {
     context._currentRenderer = null;
     context._currentRenderer2 = null;