Refactor file_store to use smart pointers

Bug: b/119276649
Merge from: http://go/wvgerrit/66367
Test: Android, CE CDM, Linux unit tests

The FileSystem interface as it exists expects an Open for a file and
then a Close when finished. However, the Close doesn't delete the file
itself and depending on the platform, the underlying impl_ as well,
leading to a memory leak. To fix this leak as well as harden against
future memory issues, this change refactors the interface to shift away
from raw pointers and towards smart pointers.

Change-Id: I7a7132ea95cd3775796a540f510b698f4f27dd24

libwvdrmengine/cdm/util/include/file_store.h

@@ -8,6 +8,7 @@
 #define WVCDM_UTIL_FILE_STORE_H_
 
 #include <unistd.h>
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -18,18 +19,10 @@ namespace wvcdm {
 // File class. The implementation is platform dependent.
 class File {
  public:
-  virtual ssize_t Read(char* buffer, size_t bytes);
-  virtual ssize_t Write(const char* buffer, size_t bytes);
-  virtual void Close();
-
- protected:
-  class Impl;
-
-  File(Impl*);
-  virtual ~File();
-
- private:
-  Impl* impl_;
+  File() {}
+  virtual ~File() {}
+  virtual ssize_t Read(char* buffer, size_t bytes) = 0;
+  virtual ssize_t Write(const char* buffer, size_t bytes) = 0;
 
   friend class FileSystem;
   CORE_DISALLOW_COPY_AND_ASSIGN(File);
@@ -37,6 +30,10 @@ class File {
 
 class FileSystem {
  public:
+  FileSystem();
+  FileSystem(const std::string& origin, void* extra_data);
+  virtual ~FileSystem();
+
   class Impl;
 
   // defines as bit flag
@@ -47,11 +44,7 @@ class FileSystem {
     kTruncate = 4
   };
 
-  FileSystem();
-  FileSystem(const std::string& origin, void* extra_data);
-  virtual ~FileSystem();
-
-  virtual File* Open(const std::string& file_path, int flags);
+  virtual std::unique_ptr<File> Open(const std::string& file_path, int flags);
 
   virtual bool Exists(const std::string& file_path);
   virtual bool Remove(const std::string& file_path);
@@ -63,14 +56,14 @@ class FileSystem {
                     std::vector<std::string>* names);
 
   const std::string& origin() const { return origin_; }
-  void SetOrigin(const std::string& origin);
+  void set_origin(const std::string& origin);
 
   const std::string& identifier() const { return identifier_; }
-  void SetIdentifier(const std::string& identifier);
+  void set_identifier(const std::string& identifier);
   bool IsGlobal() const { return identifier_.empty(); }
 
  private:
-  Impl* impl_;
+  std::unique_ptr<FileSystem::Impl> impl_;
   std::string origin_;
   std::string identifier_;