Verify MediaKeys parameter values consistently

Source/modules/encryptedmedia/MediaKeys.cpp

Index: Source/modules/encryptedmedia/MediaKeys.cpp
diff --git a/Source/modules/encryptedmedia/MediaKeys.cpp b/Source/modules/encryptedmedia/MediaKeys.cpp
index d0e173a96c1859077feaaf9cfdbc00005c6e1bb6..54553353ef7b8fbc2614504c8851f430bda522da 100644
--- a/Source/modules/encryptedmedia/MediaKeys.cpp
+++ b/Source/modules/encryptedmedia/MediaKeys.cpp
@@ -53,7 +53,7 @@ PassRefPtrWillBeRawPtr<MediaKeys> MediaKeys::create(ExecutionContext* context, c
     }
 
     // 2. If keySystem is not one of the user agent's supported Key Systems, throw a NotSupportedError and abort these steps.
-    if (!ContentDecryptionModule::supportsKeySystem(keySystem)) {
+    if (!isTypeSupported(keySystem, "")) {

[ddorwin, 2014/02/27 22:44:13]

I don't think we should use the public function for either of these things.
Among other things, we get a log message as if the application made the call.
There might also be logic that we don't need/doesn't make sense.

What we should probably do is encapsulate line 144 in a function -
isSupportedKeySystem() - and call that here and there. That function can
ASSERT(!keySystem.empty()) since callers should have checked that. This is a
super simple wrapper that we would normally avoid, but it helps with the
algorithms, avoiding calling the parent function and encapsulating what internal
function we call to actually check.

[jrummell, 2014/02/27 23:20:00]

Done.

         exceptionState.throwDOMException(NotSupportedError, "The '" + keySystem + "' key system is not supported.");
         return nullptr;
     }
@@ -108,7 +108,7 @@ PassRefPtrWillBeRawPtr<MediaKeySession> MediaKeys::createSession(ExecutionContex
 
     // 1. If type contains a MIME type that is not supported or is not supported by the keySystem,
     // throw a NOT_SUPPORTED_ERR exception and abort these steps.
-    if (!m_cdm->supportsMIMEType(contentType)) {
+    if (!isTypeSupported(m_keySystem, contentType)) {

[ddorwin, 2014/02/27 22:44:13]

~Ditto, except maybe step 4 of IST gets encapsulated.

[jrummell, 2014/02/27 23:20:00]

Done.

         exceptionState.throwDOMException(NotSupportedError, "The type provided ('" + contentType + "') is unsupported.");
         return nullptr;
     }