Minor type inference fixes to do with null and bottom types.

pkg/front_end/testcases/inference/block_bodied_lambdas_infer_bottom_async.dart.strong.expect

Index: pkg/front_end/testcases/inference/block_bodied_lambdas_infer_bottom_async.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference/block_bodied_lambdas_infer_bottom_async.dart.strong.expect b/pkg/front_end/testcases/inference/block_bodied_lambdas_infer_bottom_async.dart.strong.expect
new file mode 100644
index 0000000000000000000000000000000000000000..27e5f796cccee0cb4c35ff713b8ae780363e9346
--- /dev/null
+++ b/pkg/front_end/testcases/inference/block_bodied_lambdas_infer_bottom_async.dart.strong.expect
@@ -0,0 +1,59 @@
+library test;
+import self as self;
+import "dart:async" as asy;
+import "dart:core" as core;
+
+static method main() → dynamic /* originally async */ {
+  final asy::Completer<asy::FutureOr<dynamic>> :completer = asy::Completer::sync<asy::FutureOr<dynamic>>();
+  asy::FutureOr<dynamic> :return_value;
+  dynamic :async_op_then;
+  dynamic :async_op_error;
+  dynamic :await_jump_var = 0;
+  dynamic :await_ctx_var;
+  dynamic :saved_try_context_var0;
+  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
+    try {
+      #L1:
+      {
+        () → asy::Future<core::Null> f = () → asy::Future<core::Null> /* originally async */ {
+          final asy::Completer<asy::FutureOr<core::Null>> :completer = asy::Completer::sync<asy::FutureOr<core::Null>>();
+          asy::FutureOr<core::Null> :return_value;
+          dynamic :async_op_then;
+          dynamic :async_op_error;
+          dynamic :await_jump_var = 0;
+          dynamic :await_ctx_var;
+          function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
+            try {
+              #L2:
+              {
+                :return_value = null;
+                break #L2;
+              }
+              :completer.complete(:return_value);
+              return;
+            }
+            on dynamic catch(dynamic :exception, dynamic :stack_trace) {
+              :completer.completeError(:exception, :stack_trace);
+            }
+          :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
+          :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
+          asy::Future::microtask<dynamic>(:async_op);
+          return :completer.future;
+        };
+        asy::Future<dynamic> y = f.call();
+        asy::Future<core::String> z = f.call();
+        asy::_awaitHelper(f.call(), :async_op_then, :async_op_error, :async_op);
+        [yield] null;
+        core::String s = :result;
+      }
+      :completer.complete(:return_value);
+      return;
+    }
+    on dynamic catch(dynamic :exception, dynamic :stack_trace) {
+      :completer.completeError(:exception, :stack_trace);
+    }
+  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
+  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
+  asy::Future::microtask<dynamic>(:async_op);
+  return :completer.future;
+}