Hide shadow layer when border exceeds layer bounds.

Hide shadow layer when border exceeds layer bounds.

When the calculated shadow border exceeds layer bounds we should make
the layer invisible instead of clamping the shadow border like we
previously did. This matches the behavior of ui::wm::ImageGrid
where we set patches as invisible.

BUG=395949
TEST=verify that the bug is fixed with this patch.
NOTRY=TRUE

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=284949

[hshi1, 2014-07-22 20:33:59]

PTAL. @sky (OWNER), @derat (FYI)

It is known that the NinePatchLayer parameter |border| must not exceed the layer
bounds. Previously my solution is to use std::min to clamp |border| but it turns
out to be incorrect.

The new CL proposes to set shadow layer to invisible when the geometric
constraints are not satisfied. The behavior matches that in the existing
ui::wm::ImageGrid class (see ImageGrid::SetSize()).

[Daniel Erat, 2014-07-22 20:35:51]

lgtm

[sky, 2014-07-22 21:20:57]

LGTM

[hshi1, 2014-07-22 21:21:51]

The CQ bit was checked by hshi@chromium.org

[commit-bot: I haz the power, 2014-07-22 21:23:45]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/hshi@chromium.org/412643002/1

[hshi1, 2014-07-22 22:35:26]

The CQ bit was unchecked by hshi@chromium.org

[hshi1, 2014-07-22 23:08:53]

Hi, PS#2 is uploaded which separates |layer_| (not-drawn parent layer of the
shadow layer, accessible by shadow controller to adjust visibility of shadow)
from |shadow_layer_| (the actual nine-patch layer).

I realized this is necessary because the shadow controller needs to adjust
shadow visibility independently from the wm::Shadow's decision based on
geometric constraints.

After this change the layer hierarchy would be identical to that of
wm::ImageGrid where its layer is a not-drawn container and the actual shadow
layers are its children.

[hshi1, 2014-07-22 23:20:22]

The CQ bit was checked by hshi@chromium.org

[commit-bot: I haz the power, 2014-07-22 23:24:08]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/hshi@chromium.org/412643002/20001

[hshi1, 2014-07-23 16:34:00]

The CQ bit was checked by hshi@chromium.org

[commit-bot: I haz the power, 2014-07-23 16:36:16]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/hshi@chromium.org/412643002/20001

[commit-bot: I haz the power, 2014-07-23 16:38:17]

Change committed as 284949