Expose the poster image URL to WebMediaPlayer subclasses

Source/core/html/HTMLVideoElement.cpp

Index: Source/core/html/HTMLVideoElement.cpp
diff --git a/Source/core/html/HTMLVideoElement.cpp b/Source/core/html/HTMLVideoElement.cpp
index d49c28f4b93dd078de595d5ce15cf912b385a5ed..d8e4d8cb7348b427423ac66c3cf23daf7531fb2a 100644
--- a/Source/core/html/HTMLVideoElement.cpp
+++ b/Source/core/html/HTMLVideoElement.cpp
@@ -113,6 +113,9 @@ void HTMLVideoElement::parseAttribute(const QualifiedName& name, const AtomicStr
             if (renderer())
                 toRenderImage(renderer())->imageResource()->setImageResource(0);
         }
+        // Notify the player when the poster image URL changes.
+        if (player())
+            player()->setPoster(posterImageURL());
     } else
         HTMLMediaElement::parseAttribute(name, value);
 }