Fix conditionally parsing await as keyword.

runtime/vm/parser.h

Index: runtime/vm/parser.h
diff --git a/runtime/vm/parser.h b/runtime/vm/parser.h
index 3994aaae54d07806098d2c0be45074a6575cb279..d249655e9947fd59f05c10031ed9d09a4c967015 100644
--- a/runtime/vm/parser.h
+++ b/runtime/vm/parser.h
@@ -342,6 +342,7 @@ class Parser : public ValueObject {
   String* ExpectUserDefinedTypeIdentifier(const char* msg);
   String* ExpectIdentifier(const char* msg);
   bool IsLiteral(const char* literal);
+  bool IsAwaitAsKeyword();
 
   void SkipIf(Token::Kind);
   void SkipBlock();
@@ -773,6 +774,10 @@ class Parser : public ValueObject {
   // global variables.
   bool is_top_level_;
 
+  // await_is_keyword_ is true if we are parsing an async function. In this
+  // context async is not treated as identifier but as a keyword.
+  bool await_is_keyword_;
+
   // The member currently being parsed during "top level" parsing.
   MemberDesc* current_member_;