Don't set decomposed_transform_dirty_ bit dirty on appending Identity transform

Don't set decomposed_transform_dirty_ bit dirty on appending Identity transform

While appending identity transform, the |decomposed_transform_dirty_| bit need
not be set as appending identity will not affect the decomposed transform.

Adding a conditional check will prevent re-calculation of decomposed
transform on appending identity transform.

CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

[vivekg, 2015-06-09 14:32:26]

vivekg@chromium.org changed reviewers:
+ vivekg@chromium.org

[vivekg, 2015-06-09 14:32:27]

This looks good to me. Can we have a unit test for this change?

[vivekg, 2015-06-09 17:08:20]

vivekg@chromium.org changed reviewers:
+ danakj@chromium.org

[vivekg, 2015-06-09 17:08:20]

Adding danakj@ who is one of the OWNERs of cc/

[danakj, 2015-06-09 17:13:10]

danakj@chromium.org changed reviewers:
+ vollick@chromium.org
- danakj@chromium.org

[danakj, 2015-06-09 17:13:10]

-danakj +vollick