H264 Decoder: move cut off logic from Construct to ModifyRefPicList().

H264 Decoder: move cut off logic from Construct to ModifyRefPicList().

The ConstructRefPicListsP/B() functions are supposed to be slice agnostic.

The cut off logic is based on per-slice num_ref_idx_lX_active_minus1 values
in the slice header, and therefore it should belong to the ModifyRefPicList()
function.

BUG=479953
TEST=verify no corruption on xfnity, trybot, vda unit test

Review URL: https://codereview.chromium.org/1318283007

Cr-Commit-Position: refs/heads/master@{#346947}
(cherry picked from commit 5e19b061b92dd718401660d1899fd56bcd8637f9)

TBR=posciak@chromium.org
NOTRY=true
NOPRESUBMIT=true

[hshi1, 2015-09-02 21:39:27]

The CQ bit was checked by hshi@chromium.org

[commit-bot: I haz the power, 2015-09-02 21:39:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1323143006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1323143006/1

[commit-bot: I haz the power, 2015-09-02 21:39:40]

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

[commit-bot: I haz the power, 2015-09-02 21:39:41]

No L-G-T-M from a valid reviewer yet. Only full committers are accepted.
Even if an L-G-T-M may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[hshi1, 2015-09-02 21:40:38]

The CQ bit was checked by hshi@chromium.org

[commit-bot: I haz the power, 2015-09-02 21:41:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1323143006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1323143006/1

[commit-bot: I haz the power, 2015-09-02 21:41:17]

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

[commit-bot: I haz the power, 2015-09-02 21:41:17]

CLs for remote refs other than refs/pending/heads/master must contain NOTRY=true
and NOPRESUBMIT=true in order for the CQ to process them

[hshi1, 2015-09-02 21:44:25]

The CQ bit was checked by hshi@chromium.org

[commit-bot: I haz the power, 2015-09-02 21:44:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1323143006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1323143006/1

[commit-bot: I haz the power, 2015-09-02 21:45:57]

Committed patchset #1 (id:1)