Update Commit and GetUpdatesResponse messages to include attachment ids.

Private function HasAttachmentNotOnServer is now tested (albeit
indirectly) by directory_commit_contribution_unittest.cc via
DirectoryCommitContribution::Build.

When displayed in about:sync, SyncEntity instances will now show any
attachment ids they contain.

This CL depends on issue 395913003.

BUG=356266,394023

Review URL: https://codereview.chromium.org/393083004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@283908 0039d316-1c4b-4281-b951-d872f2087c98
18 files changed