Update YamlIO documentation for the ScalarTraits class.
Update YamlIO documentation for the ScalarTraits class.

This patch adds the missing context parameter to the
input and output methods in ScalarTraits.

Differential Revision: http://reviews.llvm.org/D9173


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@236328 91177308-0d34-0410-b5e6-96231b3b80d8

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