Rename OperationObserver to OperationDelegate

Rename OperationObserver to OperationDelegate

This class is doing more than just an observer.
Add a default implmentation of OperationDelegate::OnFileChangedByOperation() to remove DummyOperationObserver in sync_client_unittest.cc

BUG=None
TEST=unit_tests

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=285117

[kinaba, 2014-07-23 08:30:28]

lgtm

[hashimoto, 2014-07-23 10:13:41]

The CQ bit was checked by hashimoto@chromium.org

[commit-bot: I haz the power, 2014-07-23 10:14:45]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/hashimoto@chromium.org/408143014/20001

[commit-bot: I haz the power, 2014-07-23 13:33:47]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)

[commit-bot: I haz the power, 2014-07-23 14:01:10]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-07-23 14:01:12]

Try jobs failed on following builders:
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)

[hashimoto, 2014-07-24 00:31:31]

The CQ bit was checked by hashimoto@chromium.org

[commit-bot: I haz the power, 2014-07-24 00:33:14]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/hashimoto@chromium.org/408143014/20001

[commit-bot: I haz the power, 2014-07-24 02:33:21]

Change committed as 285117