Improve filtering quality of images downsampled in 2d canvas

Improve filtering quality of images downsampled in 2d canvas

With this change, images that are downsampled with drawImage on
a 2D canvas will use mipmapping in order to produce higher quality
results. non-downsampled images will continue to use bilerp, so
performance should not be impacted in majority of use cases.

BUG=498356
TEST=fast/canvas/downsample-quality.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197217

[Justin Novosad, 2015-06-10 20:48:10]

junov@chromium.org changed reviewers:
+ senorblanco@chromium.org

[Justin Novosad, 2015-06-10 20:48:11]

PTAL

[Justin Novosad, 2015-06-16 18:39:32]

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

[commit-bot: I haz the power, 2015-06-16 18:39:53]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1176073003/1

[Justin Novosad, 2015-06-16 19:43:46]

Senorblanco: Review ping

[Stephen White, 2015-06-16 20:13:55]

LGTM

[commit-bot: I haz the power, 2015-06-16 20:50:39]

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

[commit-bot: I haz the power, 2015-06-16 20:50:41]

Dry run: Try jobs failed on following builders:
  mac_blink_rel on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/59118)

[Justin Novosad, 2015-06-16 23:22:56]

The CQ bit was checked by junov@chromium.org

[Justin Novosad, 2015-06-16 23:22:56]

The patchset sent to the CQ was uploaded after l-g-t-m from
senorblanco@chromium.org
Link to the patchset: https://codereview.chromium.org/1176073003/#ps40001
(title: "re-add test")

[commit-bot: I haz the power, 2015-06-16 23:23:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1176073003/40001

[commit-bot: I haz the power, 2015-06-17 00:46:51]

Committed patchset #3 (id:40001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197217