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..a0a0aca33a31f367c5ebfe1b89565a64c568eced 100644
--- a/components/arc/test/fake_file_system_instance.cc
+++ b/components/arc/test/fake_file_system_instance.cc
@@ -4,6 +4,12 @@
 
 #include "components/arc/test/fake_file_system_instance.h"
 
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/optional.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "mojo/public/cpp/system/handle.h"
+
 namespace arc {
 
 FakeFileSystemInstance::FakeFileSystemInstance() = default;
@@ -13,20 +19,34 @@ FakeFileSystemInstance::~FakeFileSystemInstance() = default;
 void FakeFileSystemInstance::GetChildDocuments(
     const std::string& authority,
     const std::string& document_id,
-    const GetChildDocumentsCallback& callback) {}
+    const GetChildDocumentsCallback& callback) {
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE, base::Bind(callback, base::nullopt));
+}
 
 void FakeFileSystemInstance::GetDocument(const std::string& authority,
                                          const std::string& document_id,
-                                         const GetDocumentCallback& callback) {}
+                                         const GetDocumentCallback& callback) {
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE, base::Bind(callback, base::Passed(mojom::DocumentPtr())));
+}
 
 void FakeFileSystemInstance::GetFileSize(const std::string& url,
-                                         const GetFileSizeCallback& callback) {}
+                                         const GetFileSizeCallback& callback) {
+  base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE,
+                                                base::Bind(callback, -1));
+}
 
 void FakeFileSystemInstance::OpenFileToRead(
     const std::string& url,
-    const OpenFileToReadCallback& callback) {}
+    const OpenFileToReadCallback& callback) {
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE, base::Bind(callback, base::Passed(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