Add a compositing display item which replaces transparency display item

Add a compositing display item which replaces transparency display item

This patch adds a compositing display item which is similar to the
transparency display item (to be removed in a followup) but sports
SkXfermode (combining blendmode and compositing op) as well as
color filters. With this new object we can implement SVG masking.

See associated blink patch: https://codereview.chromium.org/947893002

Committed: https://crrev.com/ce0b702f48b229e94ee6593e58dccd6f1d690687
Cr-Commit-Position: refs/heads/master@{#317905}

[pdr., 2015-02-23 16:58:50]

pdr@chromium.org changed reviewers:
+ ajuma@chromium.org

[ajuma, 2015-02-23 18:05:33]

lgtm

[pdr., 2015-02-23 18:10:52]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2015-02-23 18:11:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/942403002/20001

[commit-bot: I haz the power, 2015-02-23 18:14:31]

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

[commit-bot: I haz the power, 2015-02-23 18:14:32]

Try jobs failed on following builders:
  ios_dbg_simulator on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)

[pdr., 2015-02-24 22:14:51]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2015-02-24 22:16:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/942403002/20001

[commit-bot: I haz the power, 2015-02-24 22:39:03]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-24 22:40:15]

Patchset 2 (id:??) landed as
https://crrev.com/ce0b702f48b229e94ee6593e58dccd6f1d690687
Cr-Commit-Position: refs/heads/master@{#317905}