Use ILLEGAL_MODE macro to silence clang error.

Use ILLEGAL_MODE macro to silence clang error.

This fixes the following clang error:

../../tests/XfermodeTest.cpp:43:44: error: comparison of constant -1 with expression of type 'SkXfermode::Mode' is always false [-Werror,-Wtautological-constant-out-of-range-compare]
    REPORTER_ASSERT(reporter, reportedMode == -1);
                                  ~~~~~~~~~~~~ ^  ~~

R=vandebo@chromium.org,reed@google.com

Committed: https://code.google.com/p/skia/source/detail?r=8692

[vandebo (ex-Chrome), 2013-04-12 16:34:47]

If I understand correctly, the test is right and the clang error is wrong.  Can
you report this upstream with clang?

Also, I don't see where ILLEGAL_MODE is coming from in your fix.  Did you add it
in another file and forget to add the other file?

[tfarina, 2013-04-12 16:47:35]

On 2013/04/12 16:34:47, vandebo wrote:
> If I understand correctly, the test is right and the clang error is wrong. 
Can
> you report this upstream with clang?
> 
Why you think it's wrong?

> Also, I don't see where ILLEGAL_MODE is coming from in your fix.  Did you add
it
> in another file and forget to add the other file?
See line 16 in that file.

[vandebo (ex-Chrome), 2013-04-12 16:48:30]

I understand now. LGTM

[tfarina, 2013-04-15 22:12:55]

Committed patchset #1 manually as r8692 (presubmit successful).