Add CompositingReasons to compositor layers.

Add CompositingReasons to compositor layers.

This is a re-land after first version (r202580) was reverted. The problem was
that extra invalidations occurred due to a call to SetNeedsCommit(). The
solution is to avoid calling SetNeedsCommit(), and accept that this debug info
will be stale on the impl-thread until something else commits.

BUG=240946
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=202848

[shawnsingh, 2013-05-28 23:15:43]

PTAL

This is the same patch as the last one in
https://codereview.chromium.org/15051011/ , except that it removes the
unnecessary SetNeedsCommit() and replaces it with a comment.

[jamesr, 2013-05-28 23:20:05]

code lgtm. comment seems more confusing than helpful in its current state

https://codereview.chromium.org/16023024/diff/1/cc/layers/layer.cc
File cc/layers/layer.cc (right):

https://codereview.chromium.org/16023024/diff/1/cc/layers/layer.cc#newcode756
cc/layers/layer.cc:756: // SetNeedsCommit() which causes invalidations in some
code paths.
Do you expect this to become something other than debug information in the
future?

[shawnsingh, 2013-05-28 23:23:14]

On 2013/05/28 23:20:05, jamesr wrote:
> code lgtm. comment seems more confusing than helpful in its current state
> 
> https://codereview.chromium.org/16023024/diff/1/cc/layers/layer.cc
> File cc/layers/layer.cc (right):
> 
> https://codereview.chromium.org/16023024/diff/1/cc/layers/layer.cc#newcode756
> cc/layers/layer.cc:756: // SetNeedsCommit() which causes invalidations in some
> code paths.
> Do you expect this to become something other than debug information in the
> future?

As far as I can see, I think it should always remain debug info.  I'll just
remove the comment.

[commit-bot: I haz the power, 2013-05-29 03:45:54]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/shawnsingh@chromium.org/16023024/4011

[commit-bot: I haz the power, 2013-05-29 11:48:51]

Change committed as 202848