Implement Cdm::listStoredLicenses()

[ Merge of http://go/wvgerrit/23600 ]

This adds a new entry to IStorage:: -

  bool list(std::vector<std::string> file_names)

It returns the name of each file in the (origin-specific) file system.

b/34628115

Uses the current file system (origin-specific) bound to the CDM. Returns
the list of stored licenses (key_set_ids) in vector output parameter.

Test: verified by unittests on angler.

Change-Id: I988556b27c2a4b75f52b59bcd78cfeaddd649acd

libwvdrmengine/cdm/core/include/device_files.h

@@ -7,6 +7,7 @@
 
 #include <set>
 #include <string>
+#include <vector>
 
 #include "device_files.pb.h"
 #include "scoped_ptr.h"
@@ -78,6 +79,7 @@ class DeviceFiles {
       int64_t* grace_period_end_time, CdmAppParameterMap* app_parameters,
       std::string* usage_entry);
   virtual bool DeleteLicense(const std::string& key_set_id);
+  virtual bool ListLicenses(std::vector<std::string>* key_set_ids);
   virtual bool DeleteAllFiles();
   virtual bool DeleteAllLicenses();
   virtual bool LicenseExists(const std::string& key_set_id);
@@ -143,6 +145,7 @@ class DeviceFiles {
   bool RetrieveHashedFile(const std::string& name,
                           video_widevine_client::sdk::File* file);
   bool FileExists(const std::string& name);
+  bool ListFiles(std::vector<std::string>* names);
   bool RemoveFile(const std::string& name);
   ssize_t GetFileSize(const std::string& name);