Disallow assigning a MediaSession after the resource has been selected

third_party/WebKit/Source/modules/mediasession/HTMLMediaElementMediaSession.cpp

Index: third_party/WebKit/Source/modules/mediasession/HTMLMediaElementMediaSession.cpp
diff --git a/third_party/WebKit/Source/modules/mediasession/HTMLMediaElementMediaSession.cpp b/third_party/WebKit/Source/modules/mediasession/HTMLMediaElementMediaSession.cpp
index ddcde17601ffe90911027ed7909630e6e3bda4cf..c98a2289be0a0db7753270a1a88bcb8303c869a3 100644
--- a/third_party/WebKit/Source/modules/mediasession/HTMLMediaElementMediaSession.cpp
+++ b/third_party/WebKit/Source/modules/mediasession/HTMLMediaElementMediaSession.cpp
@@ -5,6 +5,8 @@
 #include "config.h"
 #include "modules/mediasession/HTMLMediaElementMediaSession.h"
 
+#include "core/dom/ExceptionCode.h"
+
 namespace blink {
 
 MediaSession* HTMLMediaElementMediaSession::session(HTMLMediaElement& mediaElement)
@@ -14,8 +16,14 @@ MediaSession* HTMLMediaElementMediaSession::session(HTMLMediaElement& mediaEleme
     return nullptr;
 }
 
-void HTMLMediaElementMediaSession::setSession(HTMLMediaElement& mediaElement, MediaSession* session)
+void HTMLMediaElementMediaSession::setSession(HTMLMediaElement& mediaElement, MediaSession* session, ExceptionState& exceptionState)
 {
+    HTMLMediaElement::NetworkState networkState = mediaElement.networkState();
+    if (networkState == HTMLMediaElement::NETWORK_IDLE || networkState == HTMLMediaElement::NETWORK_LOADING) {
+        exceptionState.throwDOMException(InvalidStateError, "Media sessions must be assigned before a resource has been selected");

[philipj_slow, 2015/10/23 11:17:11]

Maybe say that the expected networkState is NETWORK_EMPTY or NETWORK_NO_SOURCE,
and also say what the actual networkState is? It has to be a pretty savvy web
developer to know about the resource selection algorithm and its connection to
networkState.

+        return;
+    }
+
     from(mediaElement).m_session = session;
 }