Bug 1691578 - part5 : add test cases to test the ability of reporting error for not supported media type. r=bryce,emilio

Add test cases for `DecoderDoctorDiagnostics::StoreFormatDiagnostics()`, which is used when checking the ability of whether the decoder is supported for certain type.

Differential Revision: https://phabricator.services.mozilla.com/D104475

dom/html/HTMLMediaElement.cpp

@@ -2079,6 +2079,14 @@ double HTMLMediaElement::VideoDecodeSuspendedTime() const {
   return mDecoder ? mDecoder->GetVideoDecodeSuspendedTimeInSeconds() : -1.0;
 }
 
+void HTMLMediaElement::SetFormatDiagnosticsReportForMimeType(
+    const nsAString& aMimeType, DecoderDoctorReportType aType) {
+  DecoderDoctorDiagnostics diagnostics;
+  diagnostics.SetDecoderDoctorReportType(aType);
+  diagnostics.StoreFormatDiagnostics(OwnerDoc(), aMimeType, false /* can play*/,
+                                     __func__);
+}
+
 already_AddRefed<layers::Image> HTMLMediaElement::GetCurrentImage() {
   MarkAsTainted();