[fsp] Simplify ID of provided file systems.

chrome/browser/chromeos/file_system_provider/provided_file_system.h

Index: chrome/browser/chromeos/file_system_provider/provided_file_system.h
diff --git a/chrome/browser/chromeos/file_system_provider/provided_file_system.h b/chrome/browser/chromeos/file_system_provider/provided_file_system.h
index ee5702764e4b42ee821183d775de1f8580c981b4..10aa0a93fc291a589c2f2adb75a7ab7ec7257b5b 100644
--- a/chrome/browser/chromeos/file_system_provider/provided_file_system.h
+++ b/chrome/browser/chromeos/file_system_provider/provided_file_system.h
@@ -17,14 +17,14 @@ class ProvidedFileSystem {
  public:
   ProvidedFileSystem();
   ProvidedFileSystem(const std::string& extension_id,
-                     const std::string& file_system_id,
+                     int file_system_id,
                      const std::string& file_system_name,
                      const base::FilePath& mount_path);
 
   ~ProvidedFileSystem();
 
   const std::string& extension_id() const { return extension_id_; }
-  const std::string& file_system_id() const { return file_system_id_; }
+  int file_system_id() const { return file_system_id_; }
   const std::string& file_system_name() const { return file_system_name_; }
   const base::FilePath& mount_path() const { return mount_path_; }
 
@@ -32,9 +32,8 @@ class ProvidedFileSystem {
   // ID of the extension providing this file system.
   std::string extension_id_;
 
-  // ID of the file system, used internally. Equal to the mount point name of
-  // the underlying file system.
-  std::string file_system_id_;
+  // ID of the file system, used internally.
+  int file_system_id_;
 
   // Name of the file system, can be rendered in the UI.
   std::string file_system_name_;