[es7] Implement async functions parsing

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index 6d421f23a08b703b388e215876819c4aab55a704..6185f60a169b0e553a7ff78bfbbf1962103eca82 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -2646,8 +2646,8 @@ class FunctionLiteral final : public Expression {
   class HasDuplicateParameters : public BitField<ParameterFlag, 3, 1> {};
   class IsFunction : public BitField<IsFunctionFlag, 4, 1> {};
   class EagerCompileHintBit : public BitField<EagerCompileHint, 5, 1> {};
-  class FunctionKindBits : public BitField<FunctionKind, 6, 8> {};
-  class ShouldBeUsedOnceHintBit : public BitField<ShouldBeUsedOnceHint, 15, 1> {
+  class FunctionKindBits : public BitField<FunctionKind, 6, 9> {};
+  class ShouldBeUsedOnceHintBit : public BitField<ShouldBeUsedOnceHint, 16, 1> {
   };
 };