Fix for lack of cover with background-size: cover

Fix for lack of cover with background-size: cover

We were sizing images for background-size:cover using floating
point computations, then putting the result into a LayoutUnit
then rounding down to align to pixels. The floating point
approximation might give 99.997 instead of 100.0, then the
conversion to LayoutUnit would make that 99.825 or something,
which would then be rounded to 99, leaving a 1 pixel gap when
the image should fill a 100 pixels wide space. The result is
the background color appearing behind the image.

This patch re-arranges the computation to avoid any rounding,
making the dimension of interest exactly match the target rect.

R=leviw@chromium.org
BUG=594580
Committed: https://crrev.com/3f65f0639cf80474313ad86ed43a9216a6991dd3
Cr-Commit-Position: refs/heads/master@{#382055}

[Stephen Chennney, 2016-03-17 19:46:20]

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

[Stephen Chennney, 2016-03-17 19:46:29]

https://codereview.chromium.org/1811943003/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp (right):

https://codereview.chromium.org/1811943003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/paint/BackgroundImageGeometry.cpp:115: //
positioningAreaSize.
Following the style guide makes the following code less obvious. It's really:

if (...) {
  if (...) {
  } else {
  }
} else {
  if (...) {
  } else {
  }
}

to cover the 4 cases: cover-x-bigger, cover-y-bigger, contain-x-smaller,
contain-y-smaller

[commit-bot: I haz the power, 2016-03-17 19:46:49]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1811943003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1811943003/1

[commit-bot: I haz the power, 2016-03-17 22:59:08]

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

[commit-bot: I haz the power, 2016-03-17 22:59:09]

Dry run: Try jobs failed on following builders:
  win_chromium_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[leviw_travelin_and_unemployed, 2016-03-18 18:38:09]

The CQ bit was checked by leviw@chromium.org

[leviw_travelin_and_unemployed, 2016-03-18 18:38:10]

lgtm

Schenney, you are my hero.

[commit-bot: I haz the power, 2016-03-18 18:39:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1811943003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1811943003/1

[commit-bot: I haz the power, 2016-03-18 19:53:31]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-03-18 19:55:13]

Description was changed from

==========
Fix for lack of cover with background-size: cover

We were sizing images for background-size:cover using floating
point computations, then putting the result into a LayoutUnit
then rounding down to align to pixels. The floating point
approximation might give 99.997 instead of 100.0, then the
conversion to LayoutUnit would make that 99.825 or something,
which would then be rounded to 99, leaving a 1 pixel gap when
the image should fill a 100 pixels wide space. The result is
the background color appearing behind the image.

This patch re-arranges the computation to avoid any rounding,
making the dimension of interest exactly match the target rect.

R=leviw@chromium.org
BUG=594580
==========

to

==========
Fix for lack of cover with background-size: cover

We were sizing images for background-size:cover using floating
point computations, then putting the result into a LayoutUnit
then rounding down to align to pixels. The floating point
approximation might give 99.997 instead of 100.0, then the
conversion to LayoutUnit would make that 99.825 or something,
which would then be rounded to 99, leaving a 1 pixel gap when
the image should fill a 100 pixels wide space. The result is
the background color appearing behind the image.

This patch re-arranges the computation to avoid any rounding,
making the dimension of interest exactly match the target rect.

R=leviw@chromium.org
BUG=594580

Committed: https://crrev.com/3f65f0639cf80474313ad86ed43a9216a6991dd3
Cr-Commit-Position: refs/heads/master@{#382055}
==========

[commit-bot: I haz the power, 2016-03-18 19:55:15]

Patchset 1 (id:??) landed as
https://crrev.com/3f65f0639cf80474313ad86ed43a9216a6991dd3
Cr-Commit-Position: refs/heads/master@{#382055}