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..1266a558028d2efc5e5db2801701401186e58676 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, "networkState must be NETWORK_EMPTY or NETWORK_NO_SOURCE.");
+        return;
+    }
+
     from(mediaElement).m_session = session;
 }