arc: Implement Read and GetFileSize for ARC content file system

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

Index: chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.cc
diff --git a/chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.cc b/chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.cc
index 91747997b911eaab2939a56e2bd4f001bedf4f69..bd118871d7836caca026e1ff37d1b8e11819c2ba 100644
--- a/chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.cc
+++ b/chrome/browser/chromeos/arc/fileapi/arc_content_file_system_url_util.cc
@@ -7,6 +7,7 @@
 #include "base/files/file_path.h"
 #include "chrome/browser/chromeos/fileapi/external_file_url_util.h"
 #include "net/base/escape.h"
+#include "storage/browser/fileapi/file_system_url.h"
 
 namespace arc {
 
@@ -38,4 +39,14 @@ GURL ExternalFileUrlToArcUrl(const GURL& external_file_url) {
           net::UnescapeRule::URL_SPECIAL_CHARS_EXCEPT_PATH_SEPARATORS));
 }
 
+GURL FileSystemUrlToArcUrl(const storage::FileSystemURL& url) {
+  base::FilePath virtual_path = base::FilePath::FromUTF8Unsafe(kMountPointName);
+  if (!base::FilePath(kMountPointPath)
+           .AppendRelativePath(url.path(), &virtual_path)) {
+    return GURL();
+  }
+  return ExternalFileUrlToArcUrl(
+      chromeos::VirtualPathToExternalFileURL(virtual_path));
+}
+
 }  // namespace arc