Revert of Revert of Implement DisplayList GatherPixelRefs

Revert of Revert of Implement DisplayList GatherPixelRefs (patchset #1 id:1 of https://codereview.chromium.org/1047413003/)

Reason for revert:
Break tree

Original issue's description:
> Revert of Implement DisplayList GatherPixelRefs (patchset #5 id:80001 of https://codereview.chromium.org/1045953002/)
>
> Reason for revert:
> Cause of crbug.com/472590
>
> Original issue's description:
> > Implement DisplayList GatherPixelRefs
> >
> > Take advantage of DisplayList playing back to generate SkPicture, and
> > use existing functions that gathers pixel ref from a single SkPicture.
> >
> > R=ajuma, enne, vmpstr
> > BUG=440468
> >
> > Committed: https://crrev.com/3d69b19b57904847ffec31b0f5d4f3568b5c6f35
> > Cr-Commit-Position: refs/heads/master@{#323152}
>
> TBR=enne@chromium.org,ajuma@chromium.org,vmpstr@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=440468
>
> Committed: https://crrev.com/74cb97d8d5c4e62a694c7f029a7c8c0b09e5bd92
> Cr-Commit-Position: refs/heads/master@{#323321}

TBR=enne@chromium.org,ajuma@chromium.org,vmpstr@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=440468
Committed: https://crrev.com/2f958f4157655afa8e86afb0549fafe51b79f219
Cr-Commit-Position: refs/heads/master@{#323324}

[weiliangc, 2015-04-01 20:48:48]

Created Revert of Revert of Implement DisplayList GatherPixelRefs

[commit-bot: I haz the power, 2015-04-01 20:49:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1050103003/1

[commit-bot: I haz the power, 2015-04-01 20:50:43]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-01 20:51:32]

Patchset 1 (id:??) landed as
https://crrev.com/2f958f4157655afa8e86afb0549fafe51b79f219
Cr-Commit-Position: refs/heads/master@{#323324}