Add an API to get total size of Drive cache including non-evictable ones.

components/drive/chromeos/file_system_interface.h

Index: components/drive/chromeos/file_system_interface.h
diff --git a/components/drive/chromeos/file_system_interface.h b/components/drive/chromeos/file_system_interface.h
index 92ea36234693fd0ea4e0c4ff818095c120a53d10..ee2b113dbc0373db8367c6f566d8a4c33ed2725c 100644
--- a/components/drive/chromeos/file_system_interface.h
+++ b/components/drive/chromeos/file_system_interface.h
@@ -148,7 +148,7 @@ typedef base::Callback<void(FileError error, const base::FilePath& file_path)>
 typedef base::Callback<void(bool)> FreeDiskSpaceCallback;
 
 // Used for returning result of calculated cache size.
-typedef base::Callback<void(uint64_t)> EvictableCacheSizeCallback;
+typedef base::Callback<void(int64_t)> CacheSizeCallback;
 
 // The mode of opening a file.
 enum OpenMode {
@@ -468,10 +468,14 @@ class FileSystemInterface {
       int64_t num_bytes,
       const FreeDiskSpaceCallback& callback) = 0;
 
+  // Calculates total cache size.
+  // |callback| must not be null.
+  virtual void CalculateCacheSize(const CacheSizeCallback& callback) = 0;
+
   // Calculates evictable cache size.
   // |callback| must not be null.
   virtual void CalculateEvictableCacheSize(
-      const EvictableCacheSizeCallback& callback) = 0;
+      const CacheSizeCallback& callback) = 0;
 };
 
 }  // namespace drive