Support subpixel layout for borders.

third_party/WebKit/Source/core/css/CSSProperties.in

Index: third_party/WebKit/Source/core/css/CSSProperties.in
diff --git a/third_party/WebKit/Source/core/css/CSSProperties.in b/third_party/WebKit/Source/core/css/CSSProperties.in
index a5f6e0f02718449d6f705046f9f35e26f9d21f13..57ffc8f39d7ce0043dfab0e312a1d417f359dec8 100644
--- a/third_party/WebKit/Source/core/css/CSSProperties.in
+++ b/third_party/WebKit/Source/core/css/CSSProperties.in
@@ -211,7 +211,7 @@ border-bottom-color interpolable, custom_all
 border-bottom-left-radius interpolable, initial=initialBorderRadius, converter=convertRadius, api_class=CSSPropertyAPIBorderRadius
 border-bottom-right-radius interpolable, initial=initialBorderRadius, converter=convertRadius, api_class=CSSPropertyAPIBorderRadius
 border-bottom-style type_name=EBorderStyle, initial=initialBorderStyle
-border-bottom-width interpolable, initial=initialBorderWidth, converter=convertLineWidth<unsigned>
+border-bottom-width interpolable, initial=initialBorderWidth, converter=convertLineWidth<float>

[pdr., 2017/01/24 06:57:31]

Should outline-width be changed in a similar way (as a followup)?

[Karl Øygard, 2017/01/24 22:42:58]

Yes, that would make sense.  I debated including outline-width and
column-rule-width in this patch, since their underlying data structures
now use floats, but opted against it since the changes are already quite
large.

 border-collapse inherited, independent, keyword_only, keywords=[separate|collapse], initial_keyword=separate

[pdr., 2017/01/24 06:57:31]

Some of the SVG test results seem like regressions (e.g.,
third_party/WebKit/LayoutTests/platform/mac/svg/zoom/page/zoom-background-images-expected.png).

Similarly, the zoom test results seem suspect to me (e.g.,
third_party/WebKit/LayoutTests/platform/win/fast/forms/color/color-suggestion-picker-appearance-zoom125-expected.png).
Shouldn't these get strictly better?

[Karl Øygard, 2017/01/24 22:42:58]

I'll recheck and verify that the new results are as expected.

The SVG tests in particular are a little tricky, since their views have int
sizes, and don't always fit well in with subpixel layout.  That was an
issue before this patch as well, but subpixel borders may in some cases
make it more obvious.

[Karl Øygard, 2017/01/27 20:19:27]

Yes, something's amiss here, investigating.
They look mostly fine to me, what do you see that you don't like?  The form
fields just shift around a bit, I assumed due to borders that now become
larger.  I'll admit I didn't investigate closely--I'm not sure how and where
these pickers are implemented.

[Karl Øygard, 2017/01/28 16:46:27]

I discovered one issue with repeating background images and sub-pixel
rendering.  This issue was already present, but was much less likely to be
triggered before.  I've created a separate bug report for that  in
https://bugs.chromium.org/p/chromium/issues/detail?id=686435

 border-image-outset interpolable, custom_all
 border-image-repeat custom_all
@@ -220,15 +220,15 @@ border-image-source interpolable, custom_value, typedom_types=[Image], keywords=
 border-image-width interpolable, custom_all
 border-left-color interpolable, custom_all
 border-left-style type_name=EBorderStyle, initial=initialBorderStyle
-border-left-width interpolable, initial=initialBorderWidth, converter=convertLineWidth<unsigned>
+border-left-width interpolable, initial=initialBorderWidth, converter=convertLineWidth<float>
 border-right-color interpolable, custom_all
 border-right-style type_name=EBorderStyle, initial=initialBorderStyle
-border-right-width interpolable, initial=initialBorderWidth, converter=convertLineWidth<unsigned>
+border-right-width interpolable, initial=initialBorderWidth, converter=convertLineWidth<float>
 border-top-color interpolable, custom_all
 border-top-left-radius interpolable, initial=initialBorderRadius, converter=convertRadius, api_class=CSSPropertyAPIBorderRadius
 border-top-right-radius interpolable, initial=initialBorderRadius, converter=convertRadius, api_class=CSSPropertyAPIBorderRadius
 border-top-style type_name=EBorderStyle, initial=initialBorderStyle
-border-top-width interpolable, initial=initialBorderWidth, converter=convertLineWidth<unsigned>, typedom_types=[Length], keywords=[thin|medium|thick], supports_percentage
+border-top-width interpolable, initial=initialBorderWidth, converter=convertLineWidth<float>, typedom_types=[Length], keywords=[thin|medium|thick], supports_percentage
 bottom typedom_types=[Length], keywords=[auto], supports_percentage, interpolable, initial=initialOffset, converter=convertLengthOrAuto
 box-shadow interpolable, converter=convertShadowList
 box-sizing