Revert of Pass initDataType instead of contentType on OnNeedKey().

content/renderer/media/android/webmediaplayer_android.cc

Index: content/renderer/media/android/webmediaplayer_android.cc
diff --git a/content/renderer/media/android/webmediaplayer_android.cc b/content/renderer/media/android/webmediaplayer_android.cc
index 4f8500a70608d916fbd477d1026ba7c893a5ab01..ea6ba1f0d538dcbb96d046e39c9af674aca353da 100644
--- a/content/renderer/media/android/webmediaplayer_android.cc
+++ b/content/renderer/media/android/webmediaplayer_android.cc
@@ -1483,11 +1483,11 @@
 // so we keep it as simple as possible without breaking major use cases.
 static std::string GuessInitDataType(const unsigned char* init_data,
                                      unsigned init_data_length) {
-  // Most WebM files use KeyId of 16 bytes. CENC init data is always >16 bytes.
+  // Most WebM files use KeyId of 16 bytes. MP4 init data are always >16 bytes.
   if (init_data_length == 16)
-    return "webm";
-
-  return "cenc";
+    return "video/webm";
+
+  return "video/mp4";
 }
 
 // TODO(xhwang): Report an error when there is encrypted stream but EME is