Add logging message to indicate success/failure

When debugging it is nice to knwo the reason that
requestMediaKeySystemAccess() failed.

BUG=924991

Change-Id: I352beb27f9a0c2fb82444ae92a4d740a886fa8e0
Reviewed-on: https://chromium-review.googlesource.com/c/1435219Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Commit-Queue: John Rummell <jrummell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625806}

third_party/blink/renderer/modules/encryptedmedia/navigator_request_media_key_system_access.cc

@@ -216,6 +216,8 @@ const SecurityOrigin* MediaKeySystemAccessInitializer::GetSecurityOrigin()
 
 void MediaKeySystemAccessInitializer::RequestSucceeded(
     WebContentDecryptionModuleAccess* access) {
+  DVLOG(3) << __func__;
+
   if (!IsExecutionContextValid())
     return;
 
@@ -226,6 +228,8 @@ void MediaKeySystemAccessInitializer::RequestSucceeded(
 
 void MediaKeySystemAccessInitializer::RequestNotSupported(
     const WebString& error_message) {
+  DVLOG(3) << __func__ << " error: " << error_message.Ascii();
+
   if (!IsExecutionContextValid())
     return;