Add EME support for new VP9 codec string in WebM.

media/blink/key_system_config_selector.cc

Index: media/blink/key_system_config_selector.cc
diff --git a/media/blink/key_system_config_selector.cc b/media/blink/key_system_config_selector.cc
index 5fcd5675bbc0a0218e8695e5cfb3c00ab8ae8cc2..6026675a1f3ac83dc0fdc08c3df745bc6322a16f 100644
--- a/media/blink/key_system_config_selector.cc
+++ b/media/blink/key_system_config_selector.cc
@@ -323,8 +323,11 @@ bool KeySystemConfigSelector::IsSupportedContentType(
   // contentTypes must provide a codec string unless the container implies a
   // particular codec. For EME, none of the currently supported containers
   // imply a codec, so |codecs| must be provided.
-  if (codecs.empty())
+  if (codecs.empty()) {
+    DVLOG(3) << __func__ << " KeySystemConfig for " << container_mime_type
+             << " does not specify necessary codecs.";
     return false;
+  }
 
   // Check that |container_mime_type| and |codecs| are supported by Chrome. This
   // is done primarily to validate extended codecs, but it also ensures that the