app_shell: Fix crash on chrome.runtime.getPackageDirectoryEntry for cros

storage/browser/fileapi/file_system_context.cc

Index: storage/browser/fileapi/file_system_context.cc
diff --git a/storage/browser/fileapi/file_system_context.cc b/storage/browser/fileapi/file_system_context.cc
index 4b300ef286ea800eac9f6e79fa22a9aaa5a272ec..85a9317b3e82f9553cd35d3095687f781b52ccf8 100644
--- a/storage/browser/fileapi/file_system_context.cc
+++ b/storage/browser/fileapi/file_system_context.cc
@@ -150,7 +150,6 @@ FileSystemContext::FileSystemContext(
                                                special_storage_policy,
                                                options)),
       sandbox_backend_(new SandboxFileSystemBackend(sandbox_delegate_.get())),
-      isolated_backend_(new IsolatedFileSystemBackend()),
       plugin_private_backend_(
           new PluginPrivateFileSystemBackend(file_task_runner,
                                              partition_path,
@@ -163,7 +162,6 @@ FileSystemContext::FileSystemContext(
       is_incognito_(options.is_incognito()),
       operation_runner_(new FileSystemOperationRunner(this)) {
   RegisterBackend(sandbox_backend_.get());
-  RegisterBackend(isolated_backend_.get());
   RegisterBackend(plugin_private_backend_.get());
 
   for (ScopedVector<FileSystemBackend>::const_iterator iter =
@@ -172,6 +170,16 @@ FileSystemContext::FileSystemContext(
     RegisterBackend(*iter);
   }
 
+  // If the embedder's additional backends already provide support for
+  // kFileSystemTypeNativeLocal and kFileSystemTypeNativeForPlatformApp then
+  // IsolatedFileSystemBackend does not need to handle them. For example, on
+  // Chrome OS the additional backend chromeos::FileSystemBackend handles these
+  // types.
+  isolated_backend_.reset(new IsolatedFileSystemBackend(
+      !ContainsKey(backend_map_, kFileSystemTypeNativeLocal),
+      !ContainsKey(backend_map_, kFileSystemTypeNativeForPlatformApp)));
+  RegisterBackend(isolated_backend_.get());
+
   if (quota_manager_proxy) {
     // Quota client assumes all backends have registered.
     quota_manager_proxy->RegisterClient(CreateQuotaClient(