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
std::string BaseNode::GenerateSyncableHash(
    syncable::ModelType model_type, const std::string& client_tag) {
  sync_pb::EntitySpecifics serialized_type;
  syncable::AddDefaultExtensionValue(model_type, &serialized_type);
  std::string hash_input;
  serialized_type.AppendToString(&hash_input);
  hash_input.append(client_tag);

  std::string encode_output;
  CHECK(base::Base64Encode(base::SHA1HashString(hash_input), &encode_output));
  return encode_output;
}

std::string BaseNode::GenerateSyncableHash(
    syncable::ModelType model_type, const std::string& client_tag) {
  sync_pb::EntitySpecifics serialized_type;
  syncable::AddDefaultExtensionValue(model_type, &serialized_type);
  std::string hash_input;
  serialized_type.AppendToString(&hash_input);
  hash_input.append(client_tag);

  std::string encode_output;
  CHECK(base::Base64Encode(base::SHA1HashString(hash_input), &encode_output));
  return encode_output;
}
