Revert of [Sync] Add size and crc32c to AttachmentId.

sync/internal_api/attachments/fake_attachment_downloader.cc

Index: sync/internal_api/attachments/fake_attachment_downloader.cc
diff --git a/sync/internal_api/attachments/fake_attachment_downloader.cc b/sync/internal_api/attachments/fake_attachment_downloader.cc
index 299c4184287ff8eabb82bb96265a668a0fd54969..53abc61da11ca18381381e3f7de83c0ce02d2589 100644
--- a/sync/internal_api/attachments/fake_attachment_downloader.cc
+++ b/sync/internal_api/attachments/fake_attachment_downloader.cc
@@ -25,8 +25,9 @@
   // attachment.
   scoped_refptr<base::RefCountedMemory> data(new base::RefCountedBytes());
   scoped_ptr<Attachment> attachment;
+  const uint32_t crc32c = ComputeCrc32c(data);
   attachment.reset(
-      new Attachment(Attachment::CreateFromParts(attachment_id, data)));
+      new Attachment(Attachment::CreateFromParts(attachment_id, data, crc32c)));
   base::MessageLoop::current()->PostTask(
       FROM_HERE,
       base::Bind(callback, DOWNLOAD_SUCCESS, base::Passed(&attachment)));