Update interfaces/reporting.idl (#19781)

Source: https://github.com/tidoust/reffy-reports/blob/04f50de/ed/idl/reporting.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/599417223
diff --git a/interfaces/reporting.idl b/interfaces/reporting.idl
index 05d5a42..f5370e8 100644
--- a/interfaces/reporting.idl
+++ b/interfaces/reporting.idl
@@ -5,10 +5,12 @@
 
 [Exposed=(Window,Worker)]
 interface ReportBody {
+  [Default] object toJSON();
 };
 
 [Exposed=(Window,Worker)]
 interface Report {
+  [Default] object toJSON();
   readonly attribute DOMString type;
   readonly attribute DOMString url;
   readonly attribute ReportBody? body;
@@ -33,6 +35,7 @@
 
 [Exposed=(Window,Worker)]
 interface DeprecationReportBody : ReportBody {
+  [Default] object toJSON();
   readonly attribute DOMString id;
   readonly attribute Date? anticipatedRemoval;
   readonly attribute DOMString message;
@@ -43,6 +46,7 @@
 
 [Exposed=(Window,Worker)]
 interface InterventionReportBody : ReportBody {
+  [Default] object toJSON();
   readonly attribute DOMString id;
   readonly attribute DOMString message;
   readonly attribute DOMString? sourceFile;
@@ -52,6 +56,7 @@
 
 [Exposed=(Window,Worker)]
 interface CrashReportBody : ReportBody {
+  [Default] object toJSON();
   readonly attribute DOMString? reason;
 };