Fix canvas test for Chrome 37

Fix canvas test for Chrome 37

TBR=terry@google.com,blois@google.com

Committed: https://code.google.com/p/dart/source/detail?r=38723

[vsm, 2014-07-30 07:34:23]

This test started failing on some platforms on Chrome 37 (both Dartium and
Dart2JS).

I suspect this is related to sub-pixel font rendering.  Changing from toInt to
ceil fixes it for me.

See:

http://build.chromium.org/p/client.dart/builders/dartium-lucid64-inc-integrat...

https://chromiumcodereview.appspot.com/423303005/diff/1/tests/html/canvasrend...
File tests/html/canvasrenderingcontext2d_test.dart (right):

https://chromiumcodereview.appspot.com/423303005/diff/1/tests/html/canvasrend...
tests/html/canvasrenderingcontext2d_test.dart:692: expectPixelUnfilled(x + width
+ 1, y);
Line 692 was failing without the change to ceil above.

https://chromiumcodereview.appspot.com/423303005/diff/1/tests/html/canvasrend...
tests/html/canvasrenderingcontext2d_test.dart:713: expectPixelUnfilled(x + width
+ 1, y);
Ditto.

[vsm, 2014-07-30 07:35:26]

Committed patchset #1 manually as r38723 (presubmit successful).

[blois, 2014-07-30 15:40:46]

lgtm