Preserve identical values for background-size and -webkit-mask-size.

Preserve identical values for background-size and -webkit-mask-size.

This patch fixes a bug where background-size/-webkit-mask-size would be
incorrectly serialized to text when the values in the pair are identical.
Setting 'background-size: 100% 100%', for example, would produce a text
representation of 'background-size: 100%', which is treated as
'background-position: 100% auto'.

For -webkit-background-size, '100%' really does mean '100% 100%', so we
maintain a policy of 'DropIdenticalValues' for this property.

BUG=364962
TEST=fast/backgrounds/size/parsing-background-sizes-values.html
     fast/masking/parsing-mask.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=172548

[ojan, 2014-04-24 01:12:38]

https://codereview.chromium.org/249803002/diff/1/Source/core/css/parser/CSSPr...
File Source/core/css/parser/CSSPropertyParser.cpp (right):

https://codereview.chromium.org/249803002/diff/1/Source/core/css/parser/CSSPr...
Source/core/css/parser/CSSPropertyParser.cpp:2849: // For backwards
compatibility.
This comment seems somewhat lacking in context. Either it should explain more or
it shouldn't be there.

Also, won't this break with line 2843 above,i.e. if you just do background-size:
100%, won't that now serialize to background-size: 100% 100% ?

[andersr, 2014-04-24 11:05:41]

https://codereview.chromium.org/249803002/diff/1/Source/core/css/parser/CSSPr...
File Source/core/css/parser/CSSPropertyParser.cpp (right):

https://codereview.chromium.org/249803002/diff/1/Source/core/css/parser/CSSPr...
Source/core/css/parser/CSSPropertyParser.cpp:2849: // For backwards
compatibility.
> it shouldn't be there.

OK, I removed it.

> won't that now serialize to background-size: 100% 100% ?

No. Line 2843 applies to -webkit-background-size, not background-size.

For background-size, a value of '100%' means '100% auto', not '100% 100%'. For
-webkit-background-size, it *does* mean '100% 100%', which is why we use
DropIdenticalValues for this property.

[ojan, 2014-04-24 17:54:43]

lgtm

[commit-bot: I haz the power, 2014-04-24 17:55:14]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/andersr@opera.com/249803002/40001

[commit-bot: I haz the power, 2014-04-24 23:07:24]

Change committed as 172548