libwebp: cherry-pick lossless decoding fix

libwebp: cherry-pick lossless decoding fix

783a8cd Regression fix for lossless decoding

Regression fix for lossless decoding

Reported here: https://code.google.com/p/webp/issues/detail?id=239

At the beginning of method 'DecodeImageData', pixels up to
'dec->last_pixel_' are assumed to be already cached. So, at the end of
previous call to that method also, that assumption should hold true.

Hence, we should cache all pixels up to 'src' regardless of 'src_last'.

This affects lossless incremental decoding only, as that is when
src_last and src_end differ.
Note: alpha decoding is implicitly incremental, as alpha decoding of
only the rows 'y_end - y_start' happens during FinishRow() call. So, this bug
affects alpha decoding in non-incremental decoding flow as well.

This bug was introduced in: https://gerrit.chromium.org/gerrit/#/c/59716.

BUG=

Committed: https://crrev.com/a92494b71a1a99292c32bf2b363cc5cf9fe30ac9
Cr-Commit-Position: refs/heads/master@{#312966}

[jzern, 2015-01-23 21:57:55]

jzern@chromium.org changed reviewers:
+ urvang@chromium.org

[urvang, 2015-01-23 22:00:22]

The CQ bit was checked by urvang@chromium.org

[urvang, 2015-01-23 22:00:22]

lgtm

[commit-bot: I haz the power, 2015-01-23 22:02:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/872923002/1

[commit-bot: I haz the power, 2015-01-23 22:02:05]

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

[commit-bot: I haz the power, 2015-01-23 22:02:05]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM 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.

[urvang, 2015-01-23 22:27:34]

The CQ bit was checked by urvang@chromium.org

[commit-bot: I haz the power, 2015-01-23 22:29:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/872923002/1

[commit-bot: I haz the power, 2015-01-23 23:40:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-23 23:42:40]

Patchset 1 (id:??) landed as
https://crrev.com/a92494b71a1a99292c32bf2b363cc5cf9fe30ac9
Cr-Commit-Position: refs/heads/master@{#312966}