Add parsing for ambient declarations

src/ast/ast.h

Index: src/ast/ast.h
diff --git a/src/ast/ast.h b/src/ast/ast.h
index 9e5208150c5eb9e35b57235dd11facf449e84120..5259265a1abd039e3a0ebea1d4a5440b6951d95d 100644
--- a/src/ast/ast.h
+++ b/src/ast/ast.h
@@ -2941,7 +2941,9 @@ enum TypeFlagsEnum {
   kDisallowTypeParameters = 1 << 0,
   kDisallowTypeAnnotation = 1 << 1,
   kAllowSignature = 1 << 2,
-  kConstructorTypes = kDisallowTypeParameters | kDisallowTypeAnnotation
+  kDisallowBody = 1 << 3,
+  kConstructorTypes = kDisallowTypeParameters | kDisallowTypeAnnotation,
+  kAmbient = kAllowSignature | kDisallowBody
 };
 
 typedef base::Flags<TypeFlagsEnum> TypeFlags;