Cast: Update simulator tool with more inputs.

media/cast/receiver/video_decoder.cc

Index: media/cast/receiver/video_decoder.cc
diff --git a/media/cast/receiver/video_decoder.cc b/media/cast/receiver/video_decoder.cc
index 2fd11fe85413071d26bb1a680d7bb34ad23e334f..896cb0a904ca509bf21adf383d829617124c0a8c 100644
--- a/media/cast/receiver/video_decoder.cc
+++ b/media/cast/receiver/video_decoder.cc
@@ -184,9 +184,14 @@ class VideoDecoder::FakeImpl : public VideoDecoder::ImplBase {
   virtual ~FakeImpl() {}
 
   virtual scoped_refptr<VideoFrame> Decode(uint8* data, int len) OVERRIDE {
+    // Make sure this is a JSON string.
+    if (!len || data[0] != '{')
+      return NULL;
     base::JSONReader reader;
     scoped_ptr<base::Value> values(
-        reader.Read(base::StringPiece(reinterpret_cast<char*>(data))));
+        reader.Read(base::StringPiece(reinterpret_cast<char*>(data), len)));
+    if (!values)
+      return NULL;
     base::DictionaryValue* dict = NULL;
     values->GetAsDictionary(&dict);