Revert 102184 - [Sync] use base::Time in sync

Make EntryKernel/Entry/BaseNode use base::Time instead of int64s.

Add sync/util/time.h, with utility functions to manage the sync proto
time format.

Store times on disk in proto format instead of the local system.
This requires a database version bump (to 77).

Update SessionChangeProcessor/SessionModelAssociator
to use base::Time, too.

Remove hackish Now() function.

Remove ZeroFields() function, and instead zero-initialize in EntryKernel::EntryKernel() directly.

BUG=
TEST=

Review URL: http://codereview.chromium.org/7981006

TBR=akalin@chromium.org
Review URL: http://codereview.chromium.org/7977034

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@102186 0039d316-1c4b-4281-b951-d872f2087c98
void BaseNode::SetUnencryptedSpecifics(
    const sync_pb::EntitySpecifics& specifics) {
  syncable::ModelType type = syncable::GetModelTypeFromSpecifics(specifics);
  DCHECK_NE(syncable::UNSPECIFIED, type);
  if (GetModelType() != syncable::UNSPECIFIED) {
    DCHECK_EQ(GetModelType(), type);
  }
  unencrypted_data_.CopyFrom(specifics);
}

void BaseNode::SetUnencryptedSpecifics(
    const sync_pb::EntitySpecifics& specifics) {
  syncable::ModelType type = syncable::GetModelTypeFromSpecifics(specifics);
  DCHECK_NE(syncable::UNSPECIFIED, type);
  if (GetModelType() != syncable::UNSPECIFIED) {
    DCHECK_EQ(GetModelType(), type);
  }
  unencrypted_data_.CopyFrom(specifics);
}
