arc: Implement Read and GetFileSize for ARC content file system

chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.h

Index: chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.h
diff --git a/chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.h b/chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.h
index f5e4d944b5b20ed6a7f02214435291a5362112c0..0d8d45315199b89a8abec114a3f8bbe69e8a0c73 100644
--- a/chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.h
+++ b/chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.h
@@ -8,6 +8,10 @@
 #include "base/files/file_path.h"
 #include "url/gurl.h"
 
+namespace storage {
+class FileSystemURL;
+}
+
 namespace arc {
 
 // The name of the ARC content file system mount point.
@@ -25,6 +29,9 @@ GURL ArcUrlToExternalFileUrl(const GURL& arc_url);
 // empty GURL.
 GURL ExternalFileUrlToArcUrl(const GURL& external_file_url);
 
+// Converts a FileSystemURL to a URL which can be used within the ARC container.
+GURL FileSystemUrlToArcUrl(const storage::FileSystemURL& url);
+
 }  // namespace arc
 
 #endif  // CHROME_BROWSER_CHROMEOS_ARC_FILEAPI_ARC_CONTENT_FILE_SYSTEM_URL_UTIL_H_