Consider the start_coord in interlaced PNG

Consider the start_coord in interlaced PNG

crrev.com/2420843003 (DIFFERENT ISSUE) resulted in a slight difference
in Gold for interlaced PNGs. The new images appeared to have slid down
slightly, implying that we sampled pixels higher (earlier) in the
image.

It turns out we were not truly taking get_start_coord into account.
This CL initializes the srcRow to consider get_start_coord, and should
fix the problem/difference.
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2424353003

Committed: https://skia.googlesource.com/skia/+/e9ea349ff12f84c55766d75e36dadaa4c754105e

[scroggo_chromium, 2016-10-18 14:30:36]

Description was changed from

==========
Consider the start_coord in interlaced PNG

crrev.com/2420843003 (DIFFERENT ISSUE) resulted in a slight difference
in Gold for interlaced PNGs. The new images appeared to have slid down
slightly, implying that we sampled pixels higher (earlier) in the
image.

It turns out we were not truly taking get_start_coord into account.
This CL initializes the srcRow to consider get_start_coord, and should
fix the problem/difference.
==========

to

==========
Consider the start_coord in interlaced PNG

crrev.com/2420843003 (DIFFERENT ISSUE) resulted in a slight difference
in Gold for interlaced PNGs. The new images appeared to have slid down
slightly, implying that we sampled pixels higher (earlier) in the
image.

It turns out we were not truly taking get_start_coord into account.
This CL initializes the srcRow to consider get_start_coord, and should
fix the problem/difference.
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2424353003
==========

[scroggo_chromium, 2016-10-18 14:32:18]

scroggo@chromium.org changed reviewers:
+ msarett@google.com

[scroggo_chromium, 2016-10-18 14:32:19]

https://codereview.chromium.org/2424353003/diff/1/src/codec/SkPngCodec.cpp
File src/codec/SkPngCodec.cpp (left):

https://codereview.chromium.org/2424353003/diff/1/src/codec/SkPngCodec.cpp#ol...
src/codec/SkPngCodec.cpp:731: for (int rowNum = fFirstRow +
get_start_coord(sampleY); rowsWrittenToOutput < rowsNeeded;
Notice that I used get_start_coord to compute rowNum, but the only thing I do
with rowNum is add to it! This should've been the first clue that something was
wrong...

[msarett1, 2016-10-18 14:50:30]

msarett@chromium.org changed reviewers:
+ msarett@chromium.org

[msarett1, 2016-10-18 14:50:31]

lgtm

[scroggo, 2016-10-18 15:40:02]

The CQ bit was checked by scroggo@google.com

[commit-bot: I haz the power, 2016-10-18 15:40:13]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-18 15:40:14]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2016-10-18 21:40 UTC

[scroggo, 2016-10-18 15:41:11]

On 2016/10/18 15:40:14, commit-bot: I haz the power wrote:
> Note for Reviewers:
> The CQ is waiting for an approval.
> If you believe that the CL is not ready yet, or if you would like to L-G-T-M
> with comments then please uncheck the CQ checkbox.
> 
> Waiting for LGTM from valid reviewer(s) till 2016-10-18 21:40 UTC

LGTM

[commit-bot: I haz the power, 2016-10-18 16:14:12]

Description was changed from

==========
Consider the start_coord in interlaced PNG

crrev.com/2420843003 (DIFFERENT ISSUE) resulted in a slight difference
in Gold for interlaced PNGs. The new images appeared to have slid down
slightly, implying that we sampled pixels higher (earlier) in the
image.

It turns out we were not truly taking get_start_coord into account.
This CL initializes the srcRow to consider get_start_coord, and should
fix the problem/difference.
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2424353003
==========

to

==========
Consider the start_coord in interlaced PNG

crrev.com/2420843003 (DIFFERENT ISSUE) resulted in a slight difference
in Gold for interlaced PNGs. The new images appeared to have slid down
slightly, implying that we sampled pixels higher (earlier) in the
image.

It turns out we were not truly taking get_start_coord into account.
This CL initializes the srcRow to consider get_start_coord, and should
fix the problem/difference.
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2424353003

Committed:
https://skia.googlesource.com/skia/+/e9ea349ff12f84c55766d75e36dadaa4c754105e
==========

[commit-bot: I haz the power, 2016-10-18 16:14:13]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/e9ea349ff12f84c55766d75e36dadaa4c754105e