Use approximation when comparing Length floats in DCHECK

Use approximation when comparing Length floats in DCHECK

The original DCHECK was asserting on float equality. This was too strict
and was firing for small negligible differences. This change flattens
specified Lengths into a single float and compares them with a constant
slack allowance.

This check is intended to pick up on differences like -5 vs 0 due to
different clamping behaviour, small differences in floating point
arithmetic is fine.

BUG=649525
Committed: https://crrev.com/d932f9ab78a0e790b4228b70a48e4fc6cac31e49
Cr-Commit-Position: refs/heads/master@{#420584}

[alancutter (OOO until 2018), 2016-09-23 04:24:23]

alancutter@chromium.org changed reviewers:
+ suzyh@chromium.org

[alancutter (OOO until 2018), 2016-09-23 04:25:57]

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

[commit-bot: I haz the power, 2016-09-23 04:26:12]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[suzyh_UTC10 (ex-contributor), 2016-09-23 05:02:54]

lgtm

[alancutter (OOO until 2018), 2016-09-23 05:10:05]

The CQ bit was unchecked by alancutter@chromium.org

[alancutter (OOO until 2018), 2016-09-23 05:10:10]

The CQ bit was checked by alancutter@chromium.org

[commit-bot: I haz the power, 2016-09-23 05:10:11]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-09-23 05:41:02]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-09-23 05:42:46]

Description was changed from

==========
Use approximation when comparing Length floats in DCHECK

The original DCHECK was asserting on float equality. This was too strict
and was firing for small negligible differences. This change flattens
specified Lengths into a single float and compares them with a constant
slack allowance.

This check is intended to pick up on differences like -5 vs 0 due to
different clamping behaviour, small differences in floating point
arithmetic is fine.

BUG=649525
==========

to

==========
Use approximation when comparing Length floats in DCHECK

The original DCHECK was asserting on float equality. This was too strict
and was firing for small negligible differences. This change flattens
specified Lengths into a single float and compares them with a constant
slack allowance.

This check is intended to pick up on differences like -5 vs 0 due to
different clamping behaviour, small differences in floating point
arithmetic is fine.

BUG=649525

Committed: https://crrev.com/d932f9ab78a0e790b4228b70a48e4fc6cac31e49
Cr-Commit-Position: refs/heads/master@{#420584}
==========

[commit-bot: I haz the power, 2016-09-23 05:42:47]

Patchset 2 (id:??) landed as
https://crrev.com/d932f9ab78a0e790b4228b70a48e4fc6cac31e49
Cr-Commit-Position: refs/heads/master@{#420584}