Fix CHECK condition in ImageResource

Fix CHECK condition in ImageResource

In ImageResource, we assumed that |errorOccured()| is true only when
|m_image| is null but this was not true since |errorOccured()| can be
true when |m_image->isNull()| is true. This CL fixes the wrong CHECK
condition.

BUG=643200
TEST=n/a

[hajimehoshi, 2016-09-02 03:59:30]

Description was changed from

==========
Fix CHECK condition in ImageResource

In ImageResource, we assumed that |errorOccured()| is true only when
|m_image| is null but this was not true since |errorOccured()| can be
true when |m_image->isNull()| is true. This CL fixes the wrong CHECK
condition.

BUG=643200
TEST=n/a
R=hiroshige@chromium.org
==========

to

==========
Fix CHECK condition in ImageResource

In ImageResource, we assumed that |errorOccured()| is true only when
|m_image| is null but this was not true since |errorOccured()| can be
true when |m_image->isNull()| is true. This CL fixes the wrong CHECK
condition.

BUG=643200
TEST=n/a
==========

[hajimehoshi, 2016-09-02 03:59:30]

hajimehoshi@chromium.org changed reviewers:
+ mkwst@chromium.org

[hajimehoshi, 2016-09-02 03:59:39]

PTAL

[hiroshige, 2016-09-02 05:11:01]

> In ImageResource, we assumed that |errorOccured()| is true only when
> |m_image| is null but this was not true since |errorOccured()| can be
> true when |m_image->isNull()| is true.
When does that occur?
Can we add a unit test?

[Mike West, 2016-09-02 08:44:42]

LGTM.

[Mike West, 2016-09-02 08:45:07]

On 2016/09/02 at 08:44:42, Mike West (OOO until 29th) wrote:
> LGTM.

(Sorry, LGTM % hiroshige's note about tests.)

[Mike West, 2016-09-02 08:45:13]

mkwst@chromium.org changed required reviewers:
+ hiroshige@chromium.org

[hajimehoshi, 2016-09-02 08:55:38]

Thank you for reviewing, but we discussed offline and concluded that it is not
good to change the invariant even in the prefilnalizer. hitoshige@ will fix this
instead.