Version 2.10.0-110.5.beta

* Cherry-pick 53895b2 to beta
* Cherry-pick 433fcd0 to beta

Author: athomas

pkg/dev_compiler/lib/src/kernel/compiler.dart

@@ -867,16 +867,21 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
     var savedTopLevelClass = _classEmittingExtends;
     _classEmittingExtends = c;
 
-    // Unroll mixins.
+    // Refers to 'S' in `class C extends S`. Set this to null to avoid
+    // referencing deferred supertypes in _emitClassConstructor's JS output.
+    js_ast.Expression baseClass;
+
     if (shouldDefer(supertype)) {
       deferredSupertypes.add(runtimeStatement('setBaseClass(#, #)', [
         getBaseClass(isMixinAliasClass(c) ? 0 : mixins.length),
         emitDeferredType(supertype),
       ]));
+      // Refers to 'supertype' without any type arguments.
       supertype =
           _coreTypes.rawType(supertype.classNode, _currentLibrary.nonNullable);
+    } else {
+      baseClass = emitClassRef(supertype);
     }
-    var baseClass = emitClassRef(supertype);
 
     if (isMixinAliasClass(c)) {
       // Given `class C = Object with M [implements I1, I2 ...];`