EME: Correctly handle container-only contentType strings

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 885049c83872d0e5f80ec16863f6b8a501777af0..659f29bf118c5d03e4cd1570fa6b74fd7fa60aef 100644
--- a/media/blink/key_system_config_selector.cc
+++ b/media/blink/key_system_config_selector.cc
@@ -310,6 +310,23 @@ bool KeySystemConfigSelector::IsSupportedContentType(
     const std::string& container_mime_type,
     const std::string& codecs,
     KeySystemConfigSelector::ConfigState* config_state) {
+  // 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()) {
+    // Since the spec didn't initially require this, add an exemption for

[ddorwin, 2016/04/25 22:58:51]

If we want to exclude contentTypes without codecs once one capability has been
selected, we may need to move this to the call site where we have more context.

[jrummell, 2016/04/26 21:23:56]

Acknowledged.

+    // some existing containers to give clients time to adapt.
+    // TODO(jrummell): Remove this exemption once the number of contentTypes
+    // without codecs drops low enough (UMA added in the blink code).
+    // http://crbug.com/605661.
+    if (container_mime_type != "audio/webm" &&

[ddorwin, 2016/04/25 22:58:51]

This assumes the string is lower case, but that doesn't happen until line 342
below.

Per step 3.6, comparison is case-insensitive. Thus, we should move that up to
the top of this function, since this function covers steps 3.4-.11 per the
comment at the call site. I think the TODO below is incorrect and can be
removed.

[jrummell, 2016/04/26 21:23:56]

Done.

+        container_mime_type != "video/webm" &&
+        container_mime_type != "audio/mp4" &&
+        container_mime_type != "video/mp4") {
+      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
   // CDM cannot support codecs that Chrome does not (which could complicate the