Merge 120934 - Non-fixed length margins don't work with align=center

Merge 120934 - Non-fixed length margins don't work with align=center
https://bugs.webkit.org/show_bug.cgi?id=89626

Reviewed by Levi Weintraub.

Source/WebCore:

Tests: fast/block/negative-start-margin-align-center-percent.html
       fast/block/positive-margin-block-child-align-center-calc.html

Calling Length::value() is a bad idea as it returns the *raw* value of
the length. For percent and calculated length this is a bad idea as they
bear not relation to the actual computed length.

* rendering/RenderBox.cpp:
(WebCore::RenderBox::computeInlineDirectionMargins):
Fixed the code to use minimumValueForLength as this nicely takes care of the 'auto' case.

LayoutTests:

* fast/block/negative-start-margin-align-center-percent-expected.html: Added.
* fast/block/negative-start-margin-align-center-percent.html: Added.
* fast/block/positive-margin-block-child-align-center-calc-expected.html: Added.
* fast/block/positive-margin-block-child-align-center-calc.html: Added.


TBR=jchaffraix@webkit.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=121274