https://bugs.webkit.org/show_bug.cgi?id=90037

Reviewed by Tony Chang.

Introduce a new calc expression node - a BlendLength node. Given two Lengths and a progress
this blends them together when evaluated.

An alternative and more general approach of being able to blend two CalcExpressionNodes was
tested, but involves more memory allocations, was measurably slower, and nothing currently
would make use of the generality.

No functional change. Covered by existing tests.

* platform/CalculationValue.h:
(CalcExpressionBlendLength):
(WebCore::CalcExpressionBlendLength::CalcExpressionBlendLength):
(WebCore::CalcExpressionBlendLength::operator==):
(WebCore::CalcExpressionBlendLength::evaluate):
(WebCore):
* platform/Length.cpp:
(WebCore::Length::blendCalculation):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@123419 268f45cc-cd09-0410-ab3c-d52691b4dbfc