Sync: Attachment Store APIs for accessing attachment metadata

Introduced two new API methods to AttachmentStoreBase:
- ReadMetadata
- ReadAllMetadata

Added unimplemented overrides for these two methods into 5 classes that
derive from AttachmentStoreBase. For now the only class that has a real
implementation and unit test coverage of the new methods
is AttachmentStoreHandle.
I'll provide implementation and test coverage for all other classes
in the next change.

BUG=435205

Review URL: https://codereview.chromium.org/736093003

Cr-Commit-Position: refs/heads/master@{#305168}

1 files changed, 13 insertions, 0 deletions

diff --git a/sync/internal_api/attachments/in_memory_attachment_store.cc b/sync/internal_api/attachments/in_memory_attachment_store.cc
index c1e366d..6dbc4fa 100644
--- a/sync/internal_api/attachments/in_memory_attachment_store.cc
+++ b/sync/internal_api/attachments/in_memory_attachment_store.cc
@@ -77,4 +77,17 @@ void InMemoryAttachmentStore::Drop(const AttachmentIdList& ids,
   callback_task_runner_->PostTask(FROM_HERE, base::Bind(callback, result));
 }
 
+void InMemoryAttachmentStore::ReadMetadata(
+    const AttachmentIdList& ids,
+    const ReadMetadataCallback& callback) {
+  // TODO(stanisc): implement this.
+  NOTIMPLEMENTED();
+}
+
+void InMemoryAttachmentStore::ReadAllMetadata(
+    const ReadMetadataCallback& callback) {
+  // TODO(stanisc): implement this.
+  NOTIMPLEMENTED();
+}
+
 }  // namespace syncer