Make Isolated file system writable only if it is configured so

webkit/fileapi/sandbox_mount_point_provider.cc

Index: webkit/fileapi/sandbox_mount_point_provider.cc
diff --git a/webkit/fileapi/sandbox_mount_point_provider.cc b/webkit/fileapi/sandbox_mount_point_provider.cc
index 0c1f59f8430c0890abf24df50fab65a4dc5cdb5d..46d734b8496d18cfd4ce878af6f0667a6b20429b 100644
--- a/webkit/fileapi/sandbox_mount_point_provider.cc
+++ b/webkit/fileapi/sandbox_mount_point_provider.cc
@@ -24,6 +24,7 @@
 #include "webkit/fileapi/file_system_util.h"
 #include "webkit/fileapi/native_file_util.h"
 #include "webkit/fileapi/obfuscated_file_util.h"
+#include "webkit/fileapi/sandbox_file_stream_writer.h"
 #include "webkit/glue/webkit_glue.h"
 #include "webkit/quota/quota_manager.h"
 
@@ -461,9 +462,7 @@ fileapi::FileStreamWriter* SandboxMountPointProvider::CreateFileStreamWriter(
     const GURL& url,
     int64 offset,
     FileSystemContext* context) const {
-  // TODO(kinaba,kinuko): return SandboxFileWriter when it is implemented.
-  NOTIMPLEMENTED();
-  return NULL;
+  return new SandboxFileStreamWriter(context, url, offset);
 }
 
 FileSystemQuotaUtil* SandboxMountPointProvider::GetQuotaUtil() {