Parse await as part of an unary expression.

tests/language/await_future_test.dart

Index: tests/language/await_future_test.dart
diff --git a/tests/language/await_future_test.dart b/tests/language/await_future_test.dart
index 2652d1d5b956737b89cbbb8d5c78e1f2453b5212..54631f343f255cef3b8acc50628135f33f8323d9 100644
--- a/tests/language/await_future_test.dart
+++ b/tests/language/await_future_test.dart
@@ -70,6 +70,10 @@ nesting() async {
   }
 }
 
+awaitAsUnary(a,b) async {
+  return await a + await b;
+}
+
 awaitIf(p) async {
   if (p < (await bar(5))) {
     return "p<5";
@@ -189,5 +193,7 @@ main() async {
     Expect.equals(15, result);
     result = await awaitNestedWhile(4,6);
     Expect.equals(24, result);
+    result = await awaitAsUnary(bar(1), bar(2));
+    Expect.equals(3, result);
   }
 }