fix misc asserts and checks found by fuzzer

fix misc asserts and checks found by fuzzer

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1713383002

TBR=

Committed: https://skia.googlesource.com/skia/+/653db51b440491b0fb1908bf5a43dcc89c90044d

[reed1, 2016-02-22 14:05:59]

Description was changed from

==========
fix misc asserts and checks found by fuzzer

BUG=skia:
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...
==========

to

==========
fix misc asserts and checks found by fuzzer

BUG=skia:
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...

TBR=
==========

[reed1, 2016-02-22 14:06:02]

The CQ bit was checked by reed@google.com

[commit-bot: I haz the power, 2016-02-22 14:06:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1719913002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1719913002/1

[commit-bot: I haz the power, 2016-02-22 14:34:49]

Description was changed from

==========
fix misc asserts and checks found by fuzzer

BUG=skia:
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...

TBR=
==========

to

==========
fix misc asserts and checks found by fuzzer

BUG=skia:
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...

TBR=

Committed:
https://skia.googlesource.com/skia/+/653db51b440491b0fb1908bf5a43dcc89c90044d
==========

[commit-bot: I haz the power, 2016-02-22 14:34:50]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/653db51b440491b0fb1908bf5a43dcc89c90044d

[ethannicholas, 2016-02-22 15:42:01]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1721743002/ by ethannicholas@google.com.

The reason for reverting is: Looks to be causing failures in
LayerTreeHostFilters* tests
(https://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel....

[robertphillips, 2016-02-22 16:03:07]

The failing cc unit test is using AlphaThresholdFilters so I think the unit
square check wasn't optional.