Defer ARC file system operations while ARC is booting.

components/arc/test/fake_file_system_instance.cc

Index: components/arc/test/fake_file_system_instance.cc
diff --git a/components/arc/test/fake_file_system_instance.cc b/components/arc/test/fake_file_system_instance.cc
index d9c6f833ba5083c13de5197352ebb1af6ebae844..19237ec767d20811d4cac36ecbbf0b4a2445dcdb 100644
--- a/components/arc/test/fake_file_system_instance.cc
+++ b/components/arc/test/fake_file_system_instance.cc
@@ -4,6 +4,9 @@
 
 #include "components/arc/test/fake_file_system_instance.h"
 
+#include "base/optional.h"
+#include "mojo/public/cpp/system/handle.h"
+
 namespace arc {
 
 FakeFileSystemInstance::FakeFileSystemInstance() = default;
@@ -13,20 +16,30 @@ FakeFileSystemInstance::~FakeFileSystemInstance() = default;
 void FakeFileSystemInstance::GetChildDocuments(
     const std::string& authority,
     const std::string& document_id,
-    const GetChildDocumentsCallback& callback) {}
+    const GetChildDocumentsCallback& callback) {
+  callback.Run(base::nullopt);
+}
 
 void FakeFileSystemInstance::GetDocument(const std::string& authority,
                                          const std::string& document_id,
-                                         const GetDocumentCallback& callback) {}
+                                         const GetDocumentCallback& callback) {
+  callback.Run(mojom::DocumentPtr());
+}
 
 void FakeFileSystemInstance::GetFileSize(const std::string& url,
-                                         const GetFileSizeCallback& callback) {}
+                                         const GetFileSizeCallback& callback) {
+  callback.Run(-1);
+}
 
 void FakeFileSystemInstance::OpenFileToRead(
     const std::string& url,
-    const OpenFileToReadCallback& callback) {}
+    const OpenFileToReadCallback& callback) {
+  callback.Run(mojo::ScopedHandle());
+}
 
 void FakeFileSystemInstance::RequestMediaScan(
-    const std::vector<std::string>& paths) {}
+    const std::vector<std::string>& paths) {
+  // Do nothing and pretend we scaned them.
+}
 
 }  // namespace arc