Merge Tweaks Originating in Merge Review Comments

This merges several small changes that were made in response to
comments that arose when LMP changes were merged into the Widevine
repository's master branch.

Change-Id: Ifec968af54dbc3288f24654ec0c6ca9b5962e1aa

libwvdrmengine/cdm/core/include/initialization_data.h

@@ -13,7 +13,7 @@ class WvCdmEngineTest;
 
 class InitializationData {
  public:
-  InitializationData(const std::string& type,
+  InitializationData(const std::string& type = std::string(),
                      const CdmInitData& data = CdmInitData());
 
   bool is_supported() const { return is_cenc_ || is_webm_; }