[interpreter] Don't assume generator functions do an initial yield.

test/mjsunit/harmony/async-await-basic.js

Index: test/mjsunit/harmony/async-await-basic.js
diff --git a/test/mjsunit/harmony/async-await-basic.js b/test/mjsunit/harmony/async-await-basic.js
index b049a3ebe505f921671b0d4f3103b4b9b8407223..846baeb3fd416c068c975d2864fca5af31e78705 100644
--- a/test/mjsunit/harmony/async-await-basic.js
+++ b/test/mjsunit/harmony/async-await-basic.js
@@ -369,3 +369,10 @@ assertEqualsAsync(
     "20", () => (async(foo, { a = "0" }) => foo + a)("2", { a: undefined }));
 assertThrows(() => eval("async({ foo = 1 })"), SyntaxError);
 assertThrows(() => eval("async(a, { foo = 1 })"), SyntaxError);
+
+// https://bugs.chromium.org/p/chromium/issues/detail?id=628984
+async function gaga() {
+  let i = 1;
+  while (i-- > 0) { await 42 }
+}
+assertDoesNotThrow(gaga);