DCHECK style is cacheable in ComputedStyle::CopyNonInheritedFromCached.

DCHECK style is cacheable in ComputedStyle::CopyNonInheritedFromCached.

In ComputedStyle::CopyNonInheritedFromCached, we copy computed values
of non inherited properties from another ComputedStyle to the current
ComputedStyle. There are several DCHECKS in this function to make
sure that the style we're copying from is cacheable.

This patch replaces those DCHECKS with a single DCHECK on a new
function called MatchedPropertiesCache::IsStyleCacheable.

BUG=628043
Review-Url: https://codereview.chromium.org/2895283003
Cr-Commit-Position: refs/heads/master@{#475267}
Committed: https://chromium.googlesource.com/chromium/src/+/8cb8d28de8f2c439a50307ddc142c533c5b79e2c

[shend, 2017-05-22 23:12:32]

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

[commit-bot: I haz the power, 2017-05-22 23:13:05]

Dry run: CQ is trying da patch.

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

[shend, 2017-05-22 23:13:12]

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

[shend, 2017-05-22 23:13:36]

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

[shend, 2017-05-22 23:13:51]

Hi Alan, PTAL

[commit-bot: I haz the power, 2017-05-22 23:13:58]

Dry run: CQ is trying da patch.

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

[shend, 2017-05-22 23:19:51]

+bugsnash for FYI

[commit-bot: I haz the power, 2017-05-23 01:09:33]

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

[commit-bot: I haz the power, 2017-05-23 01:09:34]

Dry run: This issue passed the CQ dry run.

[alancutter (OOO until 2018), 2017-05-24 04:43:46]

whynotboth.gif?

[shend, 2017-05-24 05:40:57]

On 2017/05/24 at 04:43:46, alancutter wrote:
> whynotboth.gif?

the original DCHECK confused me a lot. I guess I could put it back in, but I
don't know if it adds any value.

[shend, 2017-05-24 07:38:36]

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

[commit-bot: I haz the power, 2017-05-24 07:39:04]

Dry run: CQ is trying da patch.

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

[shend, 2017-05-24 07:44:38]

Description was changed from

==========
Clarify DCHECK on zoom in ComputedStyle::CopyNonInheritedFromCached.

In ComputedStyle::CopyNonInheritedFromCached, we copy computed values
of non inherited properties from another ComputedStyle to the current
ComputedStyle. At the end of this function, we assert that the current
ComputedStyle's zoom is to InitialZoom(). However, this is confusing,
because what happens if the other ComputedStyle had a non-initial zoom?
Shouldn't the DCHECK trigger? Is the zoom somehow being reset somewhere
in this function?

We know that:
1. The current zoom is copied from the other zoom.
2. We don't modify the current zoom after that.
3. From the DCHECK, the current zoom is InitialZoom().

Thus, what the DCHECK is actually checking is that the other zoom is
equal to InitialZoom. This patch rephrases the DCHECK from a post-
condition to a pre-condition on the arguments, which is much clearer
in its intent.

BUG=628043
==========

to

==========
DCHECK style is cacheable in ComputedStyle::CopyNonInheritedFromCached.

In ComputedStyle::CopyNonInheritedFromCached, we copy computed values
of non inherited properties from another ComputedStyle to the current
ComputedStyle. There are several DCHECKS in this function to make
sure that the style we're copying from is cacheable.

This patch replaces those DCHECKS with a single DCHECK on a new
function called MatchedPropertiesCache::IsStyleCacheable.

BUG=628043
==========

[shend, 2017-05-24 08:10:13]

Hi Alan, made the changes discussed irl. PTAL?

[commit-bot: I haz the power, 2017-05-24 09:31:32]

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

[commit-bot: I haz the power, 2017-05-24 09:31:32]

Dry run: This issue passed the CQ dry run.

[alancutter (OOO until 2018), 2017-05-25 02:00:40]

lgtm

[shend, 2017-05-28 22:17:36]

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

[commit-bot: I haz the power, 2017-05-28 22:17:49]

Dry run: 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, 2017-05-29 00:01:34]

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

[commit-bot: I haz the power, 2017-05-29 00:01:36]

Dry run: This issue passed the CQ dry run.

[shend, 2017-05-29 00:16:40]

The CQ bit was checked by shend@chromium.org

[commit-bot: I haz the power, 2017-05-29 00:16:55]

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, 2017-05-29 00:20:40]

CQ is committing da patch.

Bot data: {"patchset_id": 40001, "attempt_start_ts": 1496017000934350,
"parent_rev": "87137bb41118cc187b406c52474d653c827b4029", "commit_rev":
"8cb8d28de8f2c439a50307ddc142c533c5b79e2c"}

[commit-bot: I haz the power, 2017-05-29 00:20:53]

Description was changed from

==========
DCHECK style is cacheable in ComputedStyle::CopyNonInheritedFromCached.

In ComputedStyle::CopyNonInheritedFromCached, we copy computed values
of non inherited properties from another ComputedStyle to the current
ComputedStyle. There are several DCHECKS in this function to make
sure that the style we're copying from is cacheable.

This patch replaces those DCHECKS with a single DCHECK on a new
function called MatchedPropertiesCache::IsStyleCacheable.

BUG=628043
==========

to

==========
DCHECK style is cacheable in ComputedStyle::CopyNonInheritedFromCached.

In ComputedStyle::CopyNonInheritedFromCached, we copy computed values
of non inherited properties from another ComputedStyle to the current
ComputedStyle. There are several DCHECKS in this function to make
sure that the style we're copying from is cacheable.

This patch replaces those DCHECKS with a single DCHECK on a new
function called MatchedPropertiesCache::IsStyleCacheable.

BUG=628043

Review-Url: https://codereview.chromium.org/2895283003
Cr-Commit-Position: refs/heads/master@{#475267}
Committed:
https://chromium.googlesource.com/chromium/src/+/8cb8d28de8f2c439a50307ddc142...
==========

[commit-bot: I haz the power, 2017-05-29 00:20:54]

Committed patchset #3 (id:40001) as
https://chromium.googlesource.com/chromium/src/+/8cb8d28de8f2c439a50307ddc142...