cc: Fix skewport math

cc: Fix skewport math

Previously, if the viewport ever moved farther than the skewport limits
in a single frame, the skewport math would break.  It would first
intersect with the max skewport (becoming empty) and then unioning with
the viewport (becoming the viewport).  By moving the union first, it
prevents this empty condition, leaving a valid skewport in the right
direction.

This addresses a case where prepainting wasn't happening when it should
have.

BUG=446645
Committed: https://crrev.com/23fa8b248a7ba2a743653967e598bd309822dac0
Cr-Commit-Position: refs/heads/master@{#321428}

[enne (OOO), 2015-03-18 23:07:41]

enne@chromium.org changed reviewers:
+ vmpstr@chromium.org

[enne (OOO), 2015-03-18 23:08:36]

https://codereview.chromium.org/1021663002/diff/1/cc/resources/picture_layer_...
File cc/resources/picture_layer_tiling_unittest.cc (right):

https://codereview.chromium.org/1021663002/diff/1/cc/resources/picture_layer_...
cc/resources/picture_layer_tiling_unittest.cc:604: // Shrink the skewport in all
directions.
Just added this for good measure.

https://codereview.chromium.org/1021663002/diff/1/cc/resources/picture_layer_...
cc/resources/picture_layer_tiling_unittest.cc:618: EXPECT_EQ(175,
move_skewport_far.height());
Before the patch, this is 100.

[vmpstr, 2015-03-18 23:11:51]

lgtm!

https://codereview.chromium.org/1021663002/diff/1/cc/resources/picture_layer_...
File cc/resources/picture_layer_tiling.cc (right):

https://codereview.chromium.org/1021663002/diff/1/cc/resources/picture_layer_...
cc/resources/picture_layer_tiling.cc:606:
DCHECK(skewport.Contains(visible_rect_in_content_space));
<_<

https://codereview.chromium.org/1021663002/diff/1/cc/resources/picture_layer_...
File cc/resources/picture_layer_tiling_unittest.cc (right):

https://codereview.chromium.org/1021663002/diff/1/cc/resources/picture_layer_...
cc/resources/picture_layer_tiling_unittest.cc:618: EXPECT_EQ(175,
move_skewport_far.height());
On 2015/03/18 23:08:36, enne wrote:
> Before the patch, this is 100.

Nice!

[enne (OOO), 2015-03-18 23:15:43]

The CQ bit was checked by enne@chromium.org

[enne (OOO), 2015-03-18 23:15:43]

The patchset sent to the CQ was uploaded after l-g-t-m from vmpstr@chromium.org
Link to the patchset: https://codereview.chromium.org/1021663002/#ps20001
(title: "Remove duplicate dcheck")

[commit-bot: I haz the power, 2015-03-18 23:18:08]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1021663002/20001

[commit-bot: I haz the power, 2015-03-19 00:50:19]

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

[commit-bot: I haz the power, 2015-03-19 00:50:20]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[enne (OOO), 2015-03-19 04:42:34]

The CQ bit was checked by enne@chromium.org

[commit-bot: I haz the power, 2015-03-19 04:43:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1021663002/20001

[commit-bot: I haz the power, 2015-03-19 05:50:19]

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

[commit-bot: I haz the power, 2015-03-19 05:50:20]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[vmpstr, 2015-03-19 14:46:43]

The CQ bit was checked by vmpstr@chromium.org

[commit-bot: I haz the power, 2015-03-19 14:47:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1021663002/20001

[commit-bot: I haz the power, 2015-03-19 16:00:42]

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

[commit-bot: I haz the power, 2015-03-19 16:00:43]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[vmpstr, 2015-03-19 16:26:07]

On 2015/03/19 16:00:43, I haz the power (commit-bot) wrote:
> Try jobs failed on following builders:
>   linux_chromium_chromeos_rel_ng on tryserver.chromium.linux (JOB_FAILED,
>
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

Hmm the dcheck is being triggered here:
picture_layer_tiling.cc(602)] Check failed:
skewport.Contains(visible_rect_in_content_space)

in the test

[enne (OOO), 2015-03-19 18:51:02]

The CQ bit was checked by enne@chromium.org

[enne (OOO), 2015-03-19 18:51:03]

The patchset sent to the CQ was uploaded after l-g-t-m from vmpstr@chromium.org
Link to the patchset: https://codereview.chromium.org/1021663002/#ps40001
(title: "Fix for empty viewport")

[commit-bot: I haz the power, 2015-03-19 18:51:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1021663002/40001

[commit-bot: I haz the power, 2015-03-19 20:46:00]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-03-19 20:46:54]

Patchset 3 (id:??) landed as
https://crrev.com/23fa8b248a7ba2a743653967e598bd309822dac0
Cr-Commit-Position: refs/heads/master@{#321428}