Verify pattern start values.

Verify pattern start values.

When calculating the starting x and y for a pattern it is possible to overflow
the int value. Use checked math to make sure we don't overflow.

BUG=chromium:637984
Committed: https://pdfium.googlesource.com/pdfium/+/b1f5545e34375a5947004ee92cc808b3df9d4a5b

[dsinclair, 2016-09-07 19:26:53]

The CQ bit was checked by dsinclair@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-09-07 19:27:02]

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

[dsinclair, 2016-09-07 19:27:33]

dsinclair@chromium.org changed reviewers:
+ thestig@chromium.org, tsepez@chromium.org, weili@chromium.org

[dsinclair, 2016-09-07 19:27:34]

PTAL.

[commit-bot: I haz the power, 2016-09-07 19:45:22]

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

[commit-bot: I haz the power, 2016-09-07 19:45:23]

Dry run: This issue passed the CQ dry run.

[Tom Sepez, 2016-09-07 20:52:24]

lgtm

[dsinclair, 2016-09-07 20:53:30]

The CQ bit was checked by dsinclair@chromium.org

[commit-bot: I haz the power, 2016-09-07 20:53:35]

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, 2016-09-07 20:53:53]

Description was changed from

==========
Verify pattern start values.

When calculating the starting x and y for a pattern it is possible to overflow
the int value. Use checked math to make sure we don't overflow.

BUG=chromium:637984
==========

to

==========
Verify pattern start values.

When calculating the starting x and y for a pattern it is possible to overflow
the int value. Use checked math to make sure we don't overflow.

BUG=chromium:637984

Committed:
https://pdfium.googlesource.com/pdfium/+/b1f5545e34375a5947004ee92cc808b3df9d...
==========

[commit-bot: I haz the power, 2016-09-07 20:53:54]

Committed patchset #1 (id:1) as
https://pdfium.googlesource.com/pdfium/+/b1f5545e34375a5947004ee92cc808b3df9d...

[Lei Zhang, 2016-09-07 21:44:32]

https://codereview.chromium.org/2317283002/diff/1/core/fpdfapi/fpdf_render/fp...
File core/fpdfapi/fpdf_render/fpdf_render_pattern.cpp (right):

https://codereview.chromium.org/2317283002/diff/1/core/fpdfapi/fpdf_render/fp...
core/fpdfapi/fpdf_render/fpdf_render_pattern.cpp:1152: start_x =
safeStartX.ValueOrDefault(0);
Can't these be ValueOrDie() since we know we won't die due to passing the checks
on line 1149?