Add AttachmentDownloader interface, change signature of AttachmentStore::Read

sync/api/attachments/attachment_uploader.h

Index: sync/api/attachments/attachment_uploader.h
diff --git a/sync/api/attachments/attachment_uploader.h b/sync/api/attachments/attachment_uploader.h
index 325a9e7d1f5836547dcc02a43df836880d240256..12fe1a308ad0fbe0438df55ac9feed66f8e22cb6 100644
--- a/sync/api/attachments/attachment_uploader.h
+++ b/sync/api/attachments/attachment_uploader.h
@@ -8,7 +8,6 @@
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/memory/weak_ptr.h"
 #include "sync/api/attachments/attachment.h"
 #include "sync/base/sync_export.h"
 
@@ -36,7 +35,7 @@ class SYNC_EXPORT AttachmentUploader {
   // or otherwise).
   //
   // |callback| will receive an UploadResult code and an updated AttachmentId
-  // |containing the server address of the newly uploaded attachment.
+  // containing the server address of the newly uploaded attachment.
   virtual void UploadAttachment(const Attachment& attachment,
                                 const UploadCallback& callback) = 0;
 };