Add GetURLForBrowserTab method to the external file system backend.

chrome/browser/chromeos/fileapi/file_system_backend_delegate.h

Index: chrome/browser/chromeos/fileapi/file_system_backend_delegate.h
diff --git a/chrome/browser/chromeos/fileapi/file_system_backend_delegate.h b/chrome/browser/chromeos/fileapi/file_system_backend_delegate.h
index b11c86a5ddefea8b979f70f08bffa79c3e15430d..b9086c4df981cb467636cbbb2c82208c6b1e15a2 100644
--- a/chrome/browser/chromeos/fileapi/file_system_backend_delegate.h
+++ b/chrome/browser/chromeos/fileapi/file_system_backend_delegate.h
@@ -6,9 +6,12 @@
 #define CHROME_BROWSER_CHROMEOS_FILEAPI_FILE_SYSTEM_BACKEND_DELEGATE_H_
 
 #include "base/basictypes.h"
+#include "base/callback_forward.h"
 #include "base/memory/scoped_ptr.h"
 #include "webkit/common/fileapi/file_system_types.h"
 
+class GURL;
+
 namespace base {
 class Time;
 }  // namespace base
@@ -32,6 +35,8 @@ namespace chromeos {
 // of FileSystemBackend.
 class FileSystemBackendDelegate {
  public:
+  typedef base::Callback<void(const GURL&)> URLCallback;

[mtomasz, 2014/09/04 05:30:01]

This callback is same as in storage::FileSystemBackend. How about moving it
outside of the class to the storage namespace and reusing in other places?
Especially than URLCallback sounds very generic. WDYT?

[hirono, 2014/09/04 06:10:59]

I agree. Done.

+
   virtual ~FileSystemBackendDelegate() {}
 
   // Called from FileSystemBackend::GetAsyncFileUtil().
@@ -55,6 +60,11 @@ class FileSystemBackendDelegate {
   // stay valid until shutdown.
   virtual storage::WatcherManager* GetWatcherManager(
       const storage::FileSystemURL& url) = 0;
+
+  // Called from FileSystemBackend::GetURLForBrowserTab.
+  virtual void GetURLForBrowserTab(
+      const storage::FileSystemURL& url,
+      const URLCallback& callback) = 0;
 };
 
 }  // namespace chromeos