Extract external file systems handling from isolated context.

chrome/browser/extensions/api/file_system/file_system_api.cc

Index: chrome/browser/extensions/api/file_system/file_system_api.cc
diff --git a/chrome/browser/extensions/api/file_system/file_system_api.cc b/chrome/browser/extensions/api/file_system/file_system_api.cc
index 2b5301ba64879af981a47efee66c46af30db8eb8..0faa9e9c3b71f42d206222e3fa8459d518a61bf1 100644
--- a/chrome/browser/extensions/api/file_system/file_system_api.cc
+++ b/chrome/browser/extensions/api/file_system/file_system_api.cc
@@ -156,10 +156,10 @@ bool GetFilePathOfFileEntry(const std::string& filesystem_name,
   FilePath relative_path = FilePath::FromUTF8Unsafe(filesystem_path);
   FilePath virtual_path = context->CreateVirtualRootPath(filesystem_id)
       .Append(relative_path);
-  if (!context->CrackIsolatedPath(virtual_path,
-                                  &filesystem_id,
-                                  NULL,
-                                  file_path)) {
+  if (!context->CrackVirtualPath(virtual_path,
+                                 &filesystem_id,
+                                 NULL,
+                                 file_path)) {
     *error = kInvalidParameters;
     return false;
   }