Fix analyzer type checking of "await" expressions.

pkg/analyzer/test/generated/resolver_test.dart

Index: pkg/analyzer/test/generated/resolver_test.dart
diff --git a/pkg/analyzer/test/generated/resolver_test.dart b/pkg/analyzer/test/generated/resolver_test.dart
index 17c8e696a023634a74404b1d2bbc045604acd6da..b2f48d04382a0649beeb4352ad8f4392a2a58870 100644
--- a/pkg/analyzer/test/generated/resolver_test.dart
+++ b/pkg/analyzer/test/generated/resolver_test.dart
@@ -9851,6 +9851,30 @@ class StaticTypeAnalyzerTest extends EngineTestCase {
     _listener.assertNoErrors();
   }
 
+  void test_visitAwaitExpression_flattened() {
+    // await e, where e has type Future<Future<int>>
+    InterfaceType intType = _typeProvider.intType;
+    InterfaceType futureIntType =
+        _typeProvider.futureType.substitute4(<DartType>[intType]);
+    InterfaceType futureFutureIntType =
+        _typeProvider.futureType.substitute4(<DartType>[futureIntType]);
+    Expression node =
+        AstFactory.awaitExpression(_resolvedVariable(futureFutureIntType, 'e'));
+    expect(_analyze(node), same(intType));
+    _listener.assertNoErrors();
+  }
+
+  void test_visitAwaitExpression_simple() {
+    // await e, where e has type Future<int>
+    InterfaceType intType = _typeProvider.intType;
+    InterfaceType futureIntType =
+        _typeProvider.futureType.substitute4(<DartType>[intType]);
+    Expression node =
+        AstFactory.awaitExpression(_resolvedVariable(futureIntType, 'e'));
+    expect(_analyze(node), same(intType));
+    _listener.assertNoErrors();
+  }
+
   void test_visitBinaryExpression_equals() {
     // 2 == 3
     Expression node = AstFactory.binaryExpression(