Fix type inference of factory constructor invocations.

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

+library test;
+import self as self;
+import "dart:async" as asy;
+import "dart:core" as core;
+import "dart:math" as math;
+
+static method main() → dynamic {
+  () → asy::Future<core::num> f = () → asy::Future<core::num> /* originally async */ {
+    final asy::Completer<asy::FutureOr<core::num>> :completer = asy::Completer::sync<asy::FutureOr<core::num>>();
+    asy::FutureOr<core::num> :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 {
+        #L1:
+        {
+          if(math::Random::•().{math::Random::nextBool}()) {
+            :return_value = 1;
+            break #L1;
+          }
+          else {
+            :return_value = 2.0;
+            break #L1;
+          }
+        }
+        :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<core::num> g = f.call();
+  asy::Future<core::int> h = f.call();
+}