Reland: Pass initDataType instead of contentType to 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 32f81d15cd5a7221a8bb2de54c6e054d64d4fd4a..0c8910d9e738ec9fa50a26c75c2440c3955c53ff 100644
--- a/content/renderer/media/android/webmediaplayer_android.cc
+++ b/content/renderer/media/android/webmediaplayer_android.cc
@@ -1498,11 +1498,11 @@ WebMediaPlayer::MediaKeyException WebMediaPlayerAndroid::generateKeyRequest(
 // 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. MP4 init data are always >16 bytes.
+  // Most WebM files use KeyId of 16 bytes. CENC init data is always >16 bytes.
   if (init_data_length == 16)
-    return "video/webm";
+    return "webm";
 
-  return "video/mp4";
+  return "cenc";
 }
 
 // TODO(xhwang): Report an error when there is encrypted stream but EME is