Avoid empty display item pairs

Avoid empty display item pairs

Seperated from https://codereview.chromium.org/892293002/ which needs
to avoid many empty BeginSubtree/EndSubtree display item pairs.

This CL can also avoid other empty pairs, to reduce the size of paint
list and unnecessary operations to be replayed.

TEST=LayerClipRecorder.Empty
R=chrishtr@chromium.org, pdr@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=189575

[Xianzhu, 2015-02-04 18:10:39]

wangxianzhu@chromium.org changed reviewers:
+ chrishtr@chromium.org, pdr@chromium.org

[chrishtr, 2015-02-04 18:21:23]

The CQ bit was checked by chrishtr@chromium.org

[chrishtr, 2015-02-04 18:21:24]

lgtm

[commit-bot: I haz the power, 2015-02-04 18:22:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/900653003/1

[commit-bot: I haz the power, 2015-02-04 18:42:06]

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

[commit-bot: I haz the power, 2015-02-04 18:42:07]

Try jobs failed on following builders:
  win_blink_compile_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_compile_dbg/bu...)

[Xianzhu, 2015-02-04 18:52:43]

We can't submit this CL until we make decision about whether to use
HashMap<DisplayItemClient, Vector<size_t>> or HashMap<DisplayItem::Id, size_t>
to lookup cached display items.

Will add more details in https://codereview.chromium.org/892293002/.

[pdr., 2015-02-04 23:07:55]

On 2015/02/04 at 18:52:43, wangxianzhu wrote:
> We can't submit this CL until we make decision about whether to use
HashMap<DisplayItemClient, Vector<size_t>> or HashMap<DisplayItem::Id, size_t>
to lookup cached display items.
> 
> Will add more details in https://codereview.chromium.org/892293002/.

I like this as well, LGTM (pending resolution on the other bug)

[Xianzhu, 2015-02-04 23:13:00]

On 2015/02/04 23:07:55, pdr wrote:
> On 2015/02/04 at 18:52:43, wangxianzhu wrote:
> > We can't submit this CL until we make decision about whether to use
> HashMap<DisplayItemClient, Vector<size_t>> or HashMap<DisplayItem::Id, size_t>
> to lookup cached display items.
> > 
> > Will add more details in https://codereview.chromium.org/892293002/.
> 
> I like this as well, LGTM (pending resolution on the other bug)

Note: This CL will break the vector-based algorithm in
https://codereview.chromium.org/892293002/ so we can't submit it for now.

[Xianzhu, 2015-02-05 00:25:54]

We can avoid the display item order implication by the new merge algorithm.

Submitting this.

[Xianzhu, 2015-02-05 05:24:11]

New patchsets have been uploaded after l-g-t-m from
chrishtr@chromium.org,pdr@chromium.org

[Xianzhu, 2015-02-05 05:24:23]

The CQ bit was checked by wangxianzhu@chromium.org

[commit-bot: I haz the power, 2015-02-05 05:25:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/900653003/20001

[commit-bot: I haz the power, 2015-02-05 07:12:46]

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

[commit-bot: I haz the power, 2015-02-05 07:12:47]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/49413)

[Xianzhu, 2015-02-05 17:00:46]

The CQ bit was checked by wangxianzhu@chromium.org

[commit-bot: I haz the power, 2015-02-05 17:02:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/900653003/20001

[Xianzhu, 2015-02-05 17:02:03]

The CQ bit was unchecked by wangxianzhu@chromium.org

[Xianzhu, 2015-02-05 17:03:11]

Committed patchset #2 (id:20001) manually as 189575 (presubmit successful).