Add the "virtual" keyword on method overrides that are missing it.

webkit/glue/plugins/pepper_video_decoder.cc

Index: webkit/glue/plugins/pepper_video_decoder.cc
diff --git a/webkit/glue/plugins/pepper_video_decoder.cc b/webkit/glue/plugins/pepper_video_decoder.cc
index cd4d3b5ca6ceae4e62e9a8b91891069c73de8f03..034974bc8fa69728769f20c20403ac38f23bb2f1 100644
--- a/webkit/glue/plugins/pepper_video_decoder.cc
+++ b/webkit/glue/plugins/pepper_video_decoder.cc
@@ -106,6 +106,10 @@ const PPB_VideoDecoder_Dev* VideoDecoder::GetInterface() {
   return &ppb_videodecoder;
 }
 
+VideoDecoder* VideoDecoder::AsVideoDecoder() {
+  return this;
+}
+
 bool VideoDecoder::Init(const PP_VideoDecoderConfig_Dev& decoder_config) {
   if (!instance())
     return false;